The intro starts it off quite nicely, and will probably be the one most people recognize as the 'Mega Man Theme' (aside from MM 3's intro or Wily Stage 1 below).
No "Okkusenman" collection can be complete without mentioning Psycho and J's high-energy J-rock version, which sounds like something X-Japan would bust out, and was used in this video, which cut this song to footage of X-Japan's final televised concert.
The music for when you get a new weapon is made of awesome. MM3just says, "I have a new power, and I'm coming to kick ass!"
I'm going to leave the original weapon get theme here since I think it's more awesome than not just any of its remixes, but any other weapon get theme in the entire series.
Cossack's 2nd theme is hands down the best fortress theme in the classic series EVER. (Complete Works version here.Remix here.) It really made you feel like you were scaling the highest parts of Cossack's fortress amidst a gathering storm.
U-GEN's remix of Blizzard Man. Also, there's a number of interesting remixes which have themed instruments based on where the robot masters actually came from—here's the link for Tomahawk Man, you can follow the links to the others.
Mega Man 6: Final Battle, because it does sound like it is the final battle, glad it wasn't though.
Castle of Evil, from the fourth and final stage. The music keeps looping itself perfectly and it sounds appropriately "chaotic", just like you expect when you're near the end.
Blade Man's Stage; It might not seem all that great to some people, as it feels like an 8-bit theme based upon a much higher-resolution soundtrack, but arrangements seem to fix this problem nicely. As always, your mileage may vary.
Aside from the Wily Base mentioned above (remixed into Enker's theme in 10), the first GB game has Wily Station.
Punk and Ballade's themes have already been linked to in the 10 section so there's no need to link it here, but it doesn't feel right not even mentioning them on their own rights.
The Wily Marine Fortress theme of Mega Man III definitely has an epic vibe to it.
From Mega Man III, this has got to be one of the best Weapon Get themes.
The Slash Man remix from Mega Man 2: The Power Fighters is pretty darn catchy.
Midboss Battle from The Power Battle, which was reused for the Yellow Devil in the sequel and as a replacement track for Wily's stage in the original Mega Man.
Bass Theme from the credits to Power Fighters is probably the best rendition of his theme yet.
Actually, that is technically an X theme, as the title of the track is "Variable X". It also plays in the dialogue scene between X and Zero in the intro stage, after Zero saves X from Vile.
You're not alone. This Mario Paint remix, in my opinion, almost bests the original theme. It's seemingly also one of the most versioned themes of that game on youtube, with variable success.
Born in the golden age of PSX music, Mega Man X4 has scarcely a weak, or even mediocre track to speak of. Favorites include Storm Owl and Jet Stingray.
Also, "The Father of All", DarkeSword's OverClocked ReMix version of X's intro theme. It's a softer melody, but tell me it doesn't get you sitting down and thinking things over all mellow-like.
The remix of Dr. Light's X1 theme... Even sadder than the SNES one...
The unused track, entitled "Armageddon", for when the space colony crashed. It sounds like a rock ballad, but there's a sense of the Earth being wiped clean...
For the Last Time, a final battle theme with a fitting name, as X5 was originally meant to be the X series' Grand Finale.
Meet Ninetails! Having your ass handed to you never sounded so awesome.
Boss/Executive Battle, the Rebellion Cadre theme. It's especially awesome and fitting when fighting Ferham.
Zero Series
Zero's theme from the first Mega Man X was so awesome that they remixed it and brought it back for the opening stage of Mega Man Zero, every bit as great (possibly even better) than ever.
Some of the best remixes for the Zero series can be found on the Mythos soundtrack. Their remixes of Departure, Enemy Hall, and Straight Ahead are highlights, but pretty much all of them are awesome.
Falling Down, the final boss music for Zero 4, and Zero's last fight in the entire series. They had to send him off in a big way, and by God did they do it!
"Departure" from Zero 2. The original is here, while a better quality remix is here. It appeared as the music for Zero's stage in Onimusha Blade Warriors, and that mix can be found here.
Another iconic theme for this series that needs to be mentioned is X, The Legend , as well as its other version, The End of Legend used only in Zero 1 when you defeat Copy X. Combine it with Copy X's broken apart body and the scene borders on Nightmare Fuel.
Snake Eyes, the final stage theme for ZX. A fitting climax.
Soul Ablaze from Advent is one of my favourite tunes from anywhere.
I consider anything to come from the Sound Create Unit at Inti Creates (called III) to be made of win. Cases in point, and these merely several examples:
Then, there's Cannon Ball. One of the single most epic battles in Mega Man history, given one of the single best themes in the series. And then? Mega Man ZX makes it BETTER. Hard Revenge, baby!
And the last song in the Gigamix is a gloriously awesome medley of every boss theme in the game, sans Trap Factory/Phantasm/Fanatics. Battle Giga Mixture.
Be Somewhere - Game Edit The anime and the games usually remain separate from each other, both in continuity and in music. But the opening theme for Stream was so awesome that they added it as the opening for the DS version of EXE 5.
I fell in love with "Digital Strider." Easily one of the best main Internet themes.
Network Transmission may have too many to count, but some of the ones that stand out for me are FireMan, PharaohMan, StarMan, and ShadowMan's stages, and the title theme, of course.
Ride On is just as notable as any theme in the series.
The Wave Road theme from 2 gave off this "you can do anything" feeling. Neither of the other WaveRoad themes in the series even came close to matching it.
Not strictly a Star Force song, but used in the advertising for SF 3, Stellar, by Kick Chop Busters (KCB).
Sometimes, when you enter an area as Mega Man in Star Force 3, the music changes to something sinister in order to alarm you about a lurking Omega Boss, aka superpowered Bosses from the other games of the series, regardless of where you are in the story. This particular music also overrides the normal battle theme, so you won't forget about the danger lurking somewhere on the Wave Road. This means that you could encounter someone crazy like Wolf Forest right at the beginning of the game. Way stronger than usual. The music in question is here.
If you're going to talk about epic remixes, you have to mention TheMegas. One of the best tracks, if not the best, on the album ("Get Equipped") is their take on Air Man's theme, "The Annihilation of Monsteropolis":
Do you know what it's like to be built this way / With only the power to push others away?
The best part of that song was Wily's ultimatum partway through.
Up in the sky / ten miles high / A man stands above the city he will destroy.
Built from airplane parts / his propeller spins as he thinks to himself / "I will destroy these people."
(And I will fly high above Monsteropolis / and I will rain terror down on the general populace.)
"For If I can't walk among them / then I will walk this world alone."
There will be a fire in the sky / And your doom will rain down!
Built from pieces of SR-71s! / and planes that crashed in World War II! / There will be a tombstone with the Planet Earth engraved on it!!
Also, Man on Fire (Heat Man)*
You are the hero! / I am the fire! / This is the meltdown! / Of your desire! / Your fight for justice turns to ashes / Meeegaaa Maaan!
, Metal Dance (Metal Man)*
You want to fight and try to be the one to bring me down / But I know that there's no chaaaance! / And I know, as soon as you step foot inside that door / You'll fall victim to my metal daaaance!
, The Quick and The Blue (Quick Man)*
Quick on the draw / in this town, I am the law! / Is what they say true? / Does death wear blue? / Can he faaaalll?
...actually, they are all unbelievably awesome.
They've just released a 4track CD based off of Mega Man 1. Their Elec Man song, 'Evolution of Circuitry', can be found on their Facebook.
Making Wily into a sympathetic, though not blameless, figure is no mean feat, and yet Look What You've Done manages it.
And who is this you send? One of them? While you cower, far from harm. He'll just disappoint you. Now it's done / We're divided / Call him home / This one's misguided. I see his hands, covered in my children's blood. And his eyes do not waver. Call me wrong? / The future needs us / Your answer's death? / You end us, bleed us And how quick you had him dispatch his brothers. You call this murderer a savior.
Mega Man IIGame Boy/Rockman World 2 isn't a very popular game in the franchise. But oh my god, this remix of the Airman stage is amazing.
There's also Magnet Man's theme from the same game, which also has been redone.
Random, aka Mega Ran, is a rapper who does (among other things) rap remixes of Mega Man tunes. They can be pretty hit or miss, but one of them is certified Awesome: Splash Woman. (The MP3 is available here.)
Thought I was in love before But I love you more, so baby, come aboard And go away with me, so I can make you see What you mean to me, and baby, we can be free... Under the sea Just you and me
And guess what? He collaborated in a song with none other than The Megas.
Hyadain2525 from Japan gives us some...interesting Alternate Character Interpretation of the Mega Man 2 Robot Masters. Some of them are really well made with some neat Easter Egg sound effects incorporated in the songs. All of them (except Crash Man being the first one made) have a little throwback refrain to the song of the robot master that is effective against them. Also they're all love songs:
From Newgrounds, there's Zero-Resurrected. His portfolio pretty much covers the entire franchise. He tends to put interesting spins on many of his themes. For a sampler:
We may already have mentioned Breis a couple of times, but here's a full playlist of all his Mega Man (X) remixes. Every single one of them is incredibly awesome.
Even Chiko's Hatedom won't deny he picks great music for his hacks. Crystal Man's stage from Rockman 5: Dood in Gate Wily's Last, for instance. Unfortunately, no one seems to know what the original is.It's Tabibito by Satomi Takasugi.
Trinitro Man (Fun fact - he was originally Nitro Man, after nitroglycerin. However, when Mega Man 10 was released with a totally different Nitro Man as a boss, he was renamed Trinitro Man - as in trinitrotoluene, or TNT.)
In Mega Man Rocks! there are a few good examples: Anchor Man, whose level is ship-based, and Hit Man, whose level is city skyline based along with Police Man who has a stage which appears to be half death trap half robot-police training center.
Also the Doujin game of Rockmen R: Dr. Wily's Counterattack - Demo - Intro Stage and although you may have to look for a Lets Play version Laserman's level, Weasleman's level, and Wily 3 are very Rockman/Mega Man PSX feeling.
Rockman no Constancy is renowned as one of the most advanced and difficult Mega Man 2 ROM hacks. It's particularly praised for its music, which is all remixes of other games, not all from Mega Man games: