Haruhi herself can be meta at times; for example, she seeks out members for the SOS Brigade based quite specifically on anime character cliches.
Chisame the computer geek in Mahou Sensei Negima!. Ironic since she herself is just as weird as any of the other characters, and getting weirder- the more she struggles to stay normal, the more bizarre stuff happens. Up to the point she becomes a semi-Magical Girl, whereupon she gets bored with reality gives up on the reality she knew and dives headfirst into the abnormal, and gives up the Meta Guy thing except in extreme cases. Such as Jack Rakan.
Being the straight man in Haré+ Guu, Haré assumes this role frequently.
A few characters played Meta Guy in Best Student Council whenever the characters seemed to remember they had no idea how Pucchan and Lance Bean (who were puppets) could think and speak of their own accord.
Gasser's case is strange in that at times, he plays this trope so straight as to loop right back in the series' weirdness. His reactions are usually so far over the top that they play a role similar to the rest of the antics.
And Lampshade Hanging. For example, remarking to himself that he gets more attention in side materials than in the main story, and refusing to go along with Milly's orders because he knows that her smiling is a great big warning sign (compare to the show, where he does whatever she asks because it's "President's Orders").
Kallen sometimes fills this role in the main series, mainly due to having a better sense of morality than most others in the main cast.
In the dubbed version of Yu-Gi-Oh! GX, Amon Garam (Adrian Gecko) takes this role in several episodes. It's around this point that the writers were getting more self-aware (or just fed up) - see also Dub Text and Who Writes This Crap?!. "The sooner I beat you, the less bad dialogue I have to hear!"
In Death Note, Ryuk frequently questions the implausibilities in Light's plans, and is in many ways an audience surrogate. In fact, he's the one that started off the entire plot, and only hangs around Light for as long as he is entertaining.
Maybe. That's not how the line was rendered in the dub, and one would think that such an important revelation wouldn't simply be dropped in the dub, so it could just be a mistaken translation, or a misinterpretation of the line itself.
Shinpachi in Gintama, as the token tsukkomi of the series, being meta is primarily his role of the series.
Brainy Smurf from the The Smurfs. Unsurprisingly, this often made him the most unpopular smurf in his village.
Sometimes, particularly when John Byrne is writing, the She-Hulk will take this role.
As will Squirrel Girl (once claiming that it was okay to break the fourth wall in recap pages, another time actually being interrupted during a recap) and her two squirrel partners, Monkey Joe and Tippy Toe.
Matthew the Raven, from The Sandman, was noted by the author as serving as a sort of mouthpiece for the audience, frequently questioning the actions of other characters who went outside the bounds of real-world common sense.
Batman's nemesis The Joker has played this role to an extent some times. One issue even had him directly addressing the audience at the start while recapping the events of the previous issue. It is apparently a canon fact that the Joker is so batshit crazy that he's actually aware of practically everything having to do with the DCU, including events of stories that haven't happened anymore and, conceivably, the fact that it's all just comic books. It's described on multiple occasions as "supersanity." The disturbing part is that this could explain the Joker's behavior in the first place; it's possible that he's a psychotic killer because he knows his actions don't matter. Nobody he hurts is real. He's beyond solipsism... and he's right. In fact, the more atrocities he commits, the more comics he appears in!
Spider-man is a more "classical" type, as he often comments on the unlikely events of the plot, how his actions go against rationality, and makes pop culture references, but he's still completely unaware of the Fourth Wall.
Empowered regularly breaks the fourth wall when she appears in the title pages of stories; Ninjette and ThugBoy lampshade this when they appear and have no idea who she's talking to.
Animal Man is an example of this trope being played mostly for drama. He was less than happy when he realized that he was a fictional character and side characters made the same realization with worse reactions.
Animal Man: Oh my God, I'm important to the plot...
Mr. Mxyzptlk often gets portrayed this way in the modern era.
You can get a similar effect from being in a Groundhog Day Loop: in the fanfiction Dr. Strangelove or how I learned to stop worrying and love the N bomb, Shinji Ikari is trapped in one of those that allows him to retry the events of the series from the telephone scene up until the End, unless he dies. After thousands of iterations in which he gleefully murdered Gendou in the very Eva bay by prog knife, by stabbing, by squirting, by drowning... etc. etc. etc. and many many other things, by the time the fic bothers to tell us the latest iteration in detail Shinji Ikari has become tougher and meaner than Duke Nukem and Johnny Montana, simplynote he starts off with the same as usual body every time through sheer brazenness brought by lots of accumulated experience and the knowledge that he doesn't have to worry about the consequences of his actions.
Kyon of course, remains the Only Sane Man within The Emiya Clan, and by extension, he takes the role of questioning the plausibility of every wacky adventure or absurdly random event that happens within the massive Multiverse the fic belongs to. He then proceeds to display knowledge of the various laws of narrative causality, and begins predicting exactly what's going to come next in the story, with stunning accuracy.
Chisame, to a lesser extent, serves as this as well. However, she can only lampshade the events, not plot the storytelling.
There's Nothing Out There is all ABOUT this trope, which is personified by its main character.
Han Solo tends to fill this trope in the original Star Wars trilogy. Some critics have complained that one of the weaknesses of the prequels is the lack of a similar character to act as the audience proxy.
Marco in Animorphs. The others often do it, but Marco makes it an art form.
Leggy Starlitz in the Bruce Sterling novel Zeitgeist is so genre savvy he uses narrative to change reality. The antagonist Greek MafiyaMagnificent Bastard, Mehmet Ozbey, discovers this power, and goes on to use Bond-style Action Hero tropes for his own nefarious purposes. Leggy's young daughter Zenobia is particularly adept. At one point she's dancing on the ceiling, saying "Look Dad! I'm being impossible!"
Live Action TV
Denny Crane of Boston Legal. He once commented about a new character, "If he was important, he'd have been in the season premiere."
Although Denny is by far the most frequent offender, everyone in Boston Legal does this from time to time. A recent episode opened with several characters worrying about whether the show had started yet.
Alan Shore is definitely the most overt Meta Guy on Boston Legal. For a relatively minor example, he wants to be on cable.
To be fair, anyone who spends any amount of time with the Doctor knows that last bit.
Professor River Song. Pretty much everything she says is a meta reference to TV or fandom in general. Spoilers anyone?
In The Sarah Jane Adventures, when The Doctor guest stars, as Matt Smith, after a minute Sarah Jane (A Tom Baker-era Companion, who met the David Tennant doctor) recognizes him, and says, "Don't you see? It's the Doctor." Jo Grant (A Pertwee-era Companion), blurts out "What Doctor? *The* Doctor? *My* Doctor?". A common trope in long term Doctor Who fandom is to refer to the actor who you first connected to in the role as 'my Doctor' (ie, 'my Doctor is Peter Davison').
One scene involved his wife joining in on the action though:
Wash: "Psychics? Really? That sounds like something out of science fiction"
Zoe: "Dear… we live on a spaceship"
In Heroes, this is (or used to be) done by, appropriately, Hiro.
Jac Naylor from Holby City is the Ur Example of this trope, but now Chantelle has fell into this trap too.
Dr. Arzt, a minor character on the show LOST who appeared near the end of the first season, was taken along with some of the main characters to find explosives, and comments on fan theories, such as why Hurley never gets thinner, or why only the main characters get to go on expeditions without consulting anyone else. Shortly afterwards, he is blown up while assuring the main characters of their safety... while holding a stick of dynamite.
Hurley has been described as "the voice of the audience" by the show's producers, and often gets these lines. Some of his comments have included "X and Y are together... who didn't see that happening?" "He's my friend, but he also has this weird other life where he does super ninja moves," various direct questions addressing plot points and, in the Season 5 premiere, a long ridiculous summary of the show's events up to that point.
Ziggy from Power Rangers RPM, with Flynn running a close second. 'Ranger Blue' opens with the entire team quizzing Doctor K on things like why their Zords have 'big, googly anime eyes', why they need to yell "RPM, get in gear!" whenever they morph, and how come things tend to spontaneously explode behind them when they do.
Martin Loyd from the anniversary episodes of Stargate SG-1. His story is that he's an alien writing a TV series (and later a movie) based on the SGC. This allows plenty of room for parodying their own mistakes.
Stargate Command (wisely) lets him continue his work, so if anybody else discovers the secret they'll be dismissed as some kook who watched the TV show.
This seems to be Jack O'Neill's job, as he does this at every opportunity.
Cameron Mitchell is stated to have read the case files of every single mission the team had ever been on before joining. This reflects Ben Browder watching all the episodes on DVD before joining the show. He hangs several lampshades on common plot devices early on.
Triple H and Shawn Michaels occasionally fall into this role under their DeGeneration X gimmick. They will very often reference long-forgotten storylines or things outside of kayfabe. In their most recent incarnation they have made reference to the Katie Vick disaster, Jeremy Piven's "Summerfest" flub, Kofi Kingston's gimmick change, and Shawn Michaels' real name. And talking about what segment of the script they were in, and that the villain of the week needed to hurry up and interrupt them so they could have their confrontation and get to commercial break.
Snake, one of Super Smash Bros Brawl's third-party characters, plays this trope fully. His mission briefings usually consist of his complete boggling of how incredibly strange the Nintendo universe actually is. Given that he's the only character whose home franchise is remotely grounded in reality (and then it's borderline No Fourth Wall), it fits him quite well.
Likewise, Slippy Toad fills this role during Fox and Falco's transmissions in the Lylat Cruse stage, noting how the characters can survive in deep space without oxygen or space suits. Peppy Hare immediately scolds him, breaking the fourth wall in the process.
The Time Goddess from Half Minute Hero. Aside from her invocation of But Thou Must when she first meets the main character in Hero 30, she also notes at the end of the "Beautiful Evil Lord" quest that the Evil Lord you just defeated/saved is noble/good-looking enough to possibly be a main character. Surely enough, the second scenario, Evil Lord 30, stars this same demon lord.
The Executor and Tradgedian of Pathologic are "stage hands" (which ties into the game's overarching theme of theatre, mostly consisting of Mind Screws and vapourizing the fourth wall). Their dialogue is full of Leaning on the Fourth Wall as a result. However, despite this claim, they are surprisingly participant in the main story: if you see them standing outside of a building in their distinctive bird masks and robes, then you know bad stuff has happened.
The Girl: So do I purchase it? Brainy: You make a choice, entirely determined by another's actions.
Xigbar takes on this role in Kingdom Hearts: Dream Drop Distance. At the height of the story's climax, he starts an exposition dump by saying, "Let's hit all these plot points in order" and openly lampshades how convoluted and wrapped up in itself the series' plot has become.
'Director' Hotti from Phoenix Wright: Ace Attorney: Justice For All, may also have 'supersanity' - he's a mental patient who is able to somehow cut into Phoenix's Inner Monologue and who is aware of the fact that the game uses static backgrounds - when you choose to examine a hospital patient on crutches, he points out that the patient hasn't moved since the last time Phoenix was there, and says 'doesn't it make you wonder if any treatment is really going on in this place?'
Embodied in the character Cherry Blossomfeather from the long-comatose comic RPG World. As the story continues, it turns out that she has a special magical skill which allows her to look beyond the boundaries of her world - which manifests in a painfully deadpan attitude and a trope spotted at least once a strip.
Relatedly (sort of), Ardam in Adventurers! does this all the time, with most other characters doing it once or twice. Eventually, he manages to turn this into a dramatic speech.
Everyone in The Order of the Stick does this from time to time. The kobold oracle does it all the time. Elan is probably the most notable example within the order. Genre Savvy is his only form of useful intelligence, and after he takes a level in Dashing Swordsman, he derives his new powers from adventure tropes.
The entire plot of 1/0 was characters debating their own existence with the author.
Though Petitus seems the most like this.
Torg of Sluggy Freelance is a fairly subtle case, always being the first one to realize when they're in stick figure filler strips and deducing the existence of the author for example. It's unclear whether this carries over to normal continuity but may be related to the fact that he's said to be unusually psychically sensitive.
Dave ends up playing this role during Act 6 Intermission 3.
Karkat has some elements of this possibly due to his ancestor's ability to remember other universes. In Karkat's very first log of Hivebent, he is confused that Gamzee can get hold of Faygo (since they are aliens), and when he meets his pre-scratch Ancestors he complains about how flat and shallow their characterisation mostly is compared to him and his friends. Kankri has a noxious variant in that he criticises the 'pr96lematic' elements of the world from inside his own universe, as if he were a sociologically-inclined fan complaining about Unfortunate Implications in his fandom on tumblr. At one point he lecturesMituna for being too much like a stereotype of The Mentally Disturbed, even though (from their perspective) Mituna cannot help acting that way.
Halo of Grrl Power. When you have superpowers and you co-own a comic book store that sells superhero comics, you get self-referential. Before she signs up as a superhero, she sits and considers whether she has any 'bad' superpowers that will plague her, like having Wolverine's regeneration so she would get seriously hurt regularly.
Quincy Archer from Survival of the Fittest is the resident Meta Guy, writing a blog about the fake SOTF and the tropes it shows, and then commenting through out the stories on the actions of the various villains and heroes. He commits suicide, but if he hadn't, one of his personal favorite villains, JR Rizzolo, would have left him to burn.
Regular Yugi is just as bad. Take for example the episode about Mai and her celebrity stalker, where almost every single line of Yugi's in that episode is him moaning and groaning about how this has absolutely nothing to do with the plot of the season and how absolutely useless it all is.
Jeff Albertson (better known as Comic Book Guy) on The Simpsons is usually the character who does this, perfectly fitting with his persona of a nerd overanalyzing comic books & cartoons.
Homer: Does anybody care what this guy thinks?
Cubert of Futurama was originally meant to fill this role, but this characteristic was dropped in later appearances after the writers realized how annoying it made him.
It also helps that his early appearances mostly involved Professor Farnsworth trying to teach his son to accept the wonders of the world, mostly through science. Futurama has an odd relationship with Status Quo Is God, and Cubert's ability to actually retain the morals of stories from episode to episode fits right in.
Craig takes on this role in the South Park "Pandemic" two-parter, with his constant cynical lampshading about the main cast's tendency to get into increasingly ridiculous situations based on a backfired plan or idea.
It's rare, but Kyle also has played this role on occasion. Perhaps the best example of this is during the episode "Butt out" when he told the boys that they could save themselves a lot of trouble if they just admitted that they chose to smoke on their own and the tobacco company had no part in the decision. He even commented that everything was following a formula and correctly predicted that he would make a speech at the end of the episode about what he learned during the episode.