Supertramp has songs, such as "School", "The Logical Song", and "Crime Of The Century", that head straight for the cynical end and never look back. However, they have songs like "Give a Little Bit" that are more idealistic.
"See the man with the lonely eyes. Take his hand, you'll be surprised..."
Nikki Sixx's "Life is Beautiful" says it right at the beginning: "Nothing like a trail of blood to find your way back home."
Morrissey of The Smiths is notorious for his cynical, jaded, navel gazing lyrics that end up somewhere on the far end of cynicism. Standouts include "Heaven Knows I'm Miserable Now", "Girlfriend in a Coma", and "That Joke Isn't Funny Anymore". Even his more romantic track, "There is a Light That Never Goes Out" is tinged with black humor.
John Lennon went to both sides quite readily. His first solo album, John Lennon/Plastic Ono Band, is generally seen as the "cynical" one, coming as it did as a result of his primal scream therapy, and his second album, Imagine, as the "idealistic" one (especially the title track) where he learned how to dress up his political statements and purging of personal demons in a way that people would accept them. (Indeed, "Imagine" is so idealistic that a lot of people miss just how radical its lyrics are.) The principle doesn't hold true for every song on the album (Imagine, for example, still includes the more cynical "Crippled Inside" and the Paul attack song "How Do You Sleep," and Plastic Ono Band has stuff like "Love") but as a whole, it's fairly accurate.
Opera has run all over the scale, depending a lot on the composer and the genre:
With Greek mythology as the typical source material, early operas were often very cynical - at least those that weren't Bowdlerized with a tacked-on Happy Ending.
Mozart's operas generally fall on the more idealistic end of the scale, with The Magic Flute as the standout among his oeuvre, but even the initially-cynical Don Giovanni ends up idealistic when the titular character's Karma Houdini Warranty runs out and he gets Dragged Off to Hell for his misdeeds. Cosi fan tutte is an exception to the rule, falling pretty far over on the cynical end despite being a comedy. The cynical Don Alfonso is proven right at the end when Fiordiligi and Dorabella are coerced into cheating on their fiancés, and pretty much no one except him ends up happy.
In Italian and French opera, whether the ending is more cynical or idealistic falls pretty strictly along dramatic/comedy lines. Even mostly light-hearted dramas usually had cynical endings. A common theme was showing two young, optimistic lovers progressing through their romance and getting closer and closer to achieving domestic bliss with each other - and then Shooting the Shaggy Dog by having one of them contract a disease and drop dead (see: La Traviata, Manon, La Bohème). Another was having one person be Driven to Suicide or murder by their lover's infidelity/cruelty/general dickishness (for example, Madame Butterfly, Carmen).
Opera in general took a hard turn for the cynical with the 20th century. Many of the titans of modern opera - Strauss's Salome and Elektra, Berg's Wozzeck and Lulu, Britten's Peter Grimes - fall on the extreme cynical end.
Pink Floyd takes an extremely cynical view on life, exemplified by albums such as Animals and The Wall. Earlier albums when Syd Barrett was part of the bad were, if not exactly idealistic, far less grim (compare The Piper at the Gates of Dawn with the previously mentioned albums).
While Lyrical Dissonance and relative obscurity give the Barenaked Ladies a reputation for whimsical cheerfulness and humour (and it's there), their actual songs and lyrics often, arguably more often than not, fall very much on the Cynical side. For example, their songs involving love are decidedly realistic, not to mention numerous songs about PTSD or depression and the like.
They can definitely slide all the way to the other side very readily, such as in "Light Up My Room".
Devo tends toward the cynical side in their concept of "De-evolution." According to former member Bob Lewis, however, there is something of an philosophical divide between the group's two frontmen, Mark Mothersbaugh and Jerry Casale:
"Gerry [sic] continues to strive for political statement and high-concept art, still maintaining some modernist, or perhaps more accurately, anti-postmodernist tendencies...Mark, on the other hand, has gained recognition for essentially commercial pursuits...his fine art prints continue to reflect his introspective highly personal aesthetic, which make their statements in a small genre manner; Mark IS postmodern." 
The Protomen. So far on the cynical side that they almost fall off the end. Yes, while singing about Mega Man.
Gorillaz is known to lean on the cynical end of the scale, in both their musical output, as demonstrated by songs like Feel Good Inc., and the band's actual lore, which is full of very cynical Black Comedy courtesy of Villain Protagonist Murdoc, an implied rapist and pedophile who is probably The Anti-Christ, and 3 other members of the band who are more moral are forced to endure suffering that's played for laughs as well as drama.
Leonard Cohen's "Diamonds In The Mine" is one of the most depressing songs in terms of cynicism, with the lyrics describing life as one Shoot the Shaggy Dog moment after another.
Oingo Boingo lands on the cynical side of the scale. In "Only a Lad", the adults blame society for the way Johnny (the "Lad" in the song") behaves, as opposed to putting him in jail for killing and stealing. "Insanity" is an eight minute indictment on the hypocrisy of the Religious Right and the dumbing down of society ("A million years of evolution, we get Danny Quayle.").
Tom Waits comes down heavily on the cynical side every single time. "Tom Traubert's Blues" (Small Change), "Rain Dogs" (Rain Dogs), "God's Away On Business" (Blood Money), you name it. He even managed to make "Heigh Ho" from Snow White bleak and dystopian in his cover of it. This may have something to do with the fact that his singing voice sounds like he routinely gargles with with his own patented blend of kerosene, gravel, and whiskey.
RunD.M.C.'s "It's Like That" from their debut album Run DMC flies all over the scale. You can't change the system, money's the most important thing you will need (when was the last time love bought you clothes?), the world seems to grow steadily crappier, life is shitty and you die - It's like that, and that's the way it is. But you shouldn't add to the misery and heartbreak life gives you - learn, don't be a fool, and help. Because it's like that, and that's the way it is.
David Bowie's creator thumbprints tend to come from the cynical end of existence — inevitable apocalypses and dystopias that can't be redeemed are common subject matter, and those who are mentally unstable, lonely, disadvantaged, and/or alienated from others have trouble finding a shoulder to cry on if they're not being outright persecuted or abused. "Black Tie White Noise" thumbs its nose at idealistic visions of race relations in favor of the Hard Truth Aesop "Racial harmony won't come without a lot of pain and violence along the way." Even his most famous love song, the title track of "Heroes", acknowledges that the love in question may not last. If there's a major optimistic message running through his body of work, it's probably "Enjoy what happiness you find while you can."
Ego Likeness is on the cynical side, often employing Humans Are the Real Monsters and Crapsack World in their songs. Burn Witch Burn, Funny Olde World, Song For Samael, Weave are good examples of this and even the somewhat uplifting Save Your Serpent have cynical lyrics.
Despite being one of, if not the, instigators of Heavy Metal, with lyrics involving dystopias and apocalyptic/satanic imagery, the band Black Sabbath and later Ozzy's solo career actually fluctuates between a middle-ground and somewhat idealistic. They might be talking about war and Satan and the end of the world, but they're talking about how war is *bad*, how Satan is going after *bad folks*, and how the end of the world *could* be. There's hope if people actually act decently to each other, but then again, their songs edge back towards cynicism with other themes.
Frightened Rabbit's the Oil Slick humorously starts on the Cynical side: the narrator wants to write a love song for his girl, but he can only write depressing songs. Halfway through, it switches to an Arcade Fire-esque section where he ultimately winds up on the idealistic side, as he realizes that the sad songs make him who he is, and he will have to own it and live through it. That section is a GIGANTIC Heartwarming Moment, especially after the depression of most of the album.
Speaking of depression, The National lie firmly on the cynical side, more so when it comes to their second album.
Jesus Christ Superstar is a very interesting case of this. It can be interpreted in virtually any position on this scale: from so far to the cynical it can be seen as a complete downer, to so far to the ideal that churches use it as their annual Easter passion play!
Power Metal is known for generally being very idealistic compared to most metal. whenever it is themed around the battle of good-versus-evil (Especially the ones with high-fantasy themes), good usually wins, though sometimes some sacrifices will have to be made along the way. Sci-fi-themed power-metal, on the other hand, is usually more cynical, generally being based around dystopian cyberpunk sorts of themes.
Radiohead leans quite cynical. Most of their songs are themed around depression, alienation and loneliness, and whatever light there is at the end of the tunnel is diffused by another layer of depression. Granted, this doesn't apply for all of their material, since "Optimistic," "Desert Island Disk,", The King of Limbs and some other material leans more optimistically.
Bad Religion is a rather interesting case in that where they stand on this scale quite literally depends on the writer. For the most part, Greg Graffin's lyrics fall more on the cynical side. While Brett Gurewitz's usually fall more on the idealistic side.
Billy Joel, with a couple exceptions (such as "New York State Of Mind" and a good portion of An Innocent Man) usually falls squarely on the cynical side of the scale.
Nirvana almost chaotically fluctuated between both ends of the scale - sometimes in the same song! While their music showed a very clear distrust for other people, it still usually had an underlying message of optimism and moving forward. Even on the Darker and EdgierIn Utero.
Alice in Chains, on the other hand, was relentlessly cynical in the 90's. In fact, their albums Dirt and Alice In Chains might as well have been called "Crapsack World: The Musical." On the other hand, the band's music with William DuVall is largely at the very middle of this scale. It's still by no means idealistic, but it does have a considerably more optimistic view of the world than their music during the Layne Staley years.
The Offspring leans very heavily on the "cynical" side. Their softer and moodier songs have a decidedly pessimistic undertone, while their harder songs are almost misanthropic in their rage at the world. Somewhat ironically, they have a song called "Cool To Hate" which actually ridicules teenage cynicism. Pot calling the kettle black, maybe?
Arcade Fire has traversed across the scale plenty during their career. Their albums deal with the struggle to find joy amidst the triteness of conformity, as well as deeper themes of life, fear, death, and making sense of contemporary society. Each of these topics are dealt with both contempt and longing, if not hope, and it's also worth noting that each album (even the relatively more cynical Neon Bible) end with a track more on the hopeful, idealistic side, but in general, they average out near the center of the scale.
tool started on the cynical end and meandered in a more idealistic direction over their career. Opiate and Aenima were full of screeds against organized religion, consumerism, and American culture, while Lateralus and 10,000 Days still have some cynical moments but take more time to praise patience, forgiveness, and understanding.
While Die Ärzte are generally on the idealistic side (even many of their sad songs end with at least a World Half Full as seen in the song Herrliche Jahre where the Protagonist in the end does get at least close to what he wants), they do have a few songs full of cynicism, especially towards the Radio as a medium love as a concept. Interestingly the live versions of some of their more cynical songs get a lot more idealistic (or plain silly) by seemingly minor text changes. Of course due to their position on the Sliding Scale of Silliness vs. Seriousness (for the most part) the songs making a serious or dark point tend to surprise casual observers.
Many of Sara Bareilles songs are very cynical, such as "Love Song" and "King of Anything?". However, there is also "Brave", which is as idealistic as can be. She also wrote the musical Waitress, based on the 2007 film of the same name, which is firmly an idealistic musical even in its darker moments.
The now split-up Porcupine Tree is almost relentlessly cynical. Nearly every song is about depression, despair, or the general shallowness/selfishness of humankind. Even songs that initially seem like they might fall more on the idealistic side (such as "The Start Of Something Beautiful") quickly turn cynical once they get going.
Reel Big Fish's catalog mainly consists of unrelentingly cynical songs about love and the music industry.
The Smashing Pumpkins veer both ways on this scale but typically settle more on the idealistic side. Though some songs take a clearly cynical stance on love, grief, etc., they still maintain an underlying message of hope and faith in humanity.
Nine Inch Nails is on the far cynical end of the scale. Many songs have subject matter like depression, isolation, and a negative outlook on the world, and even With Teeth and Hesitation Marks are more about recovery and reflections about struggles with the mind.
Red Hot Chili Peppers is usually pretty far on the idealistic side, as most of their songs have an underlying message of hope, compassion and/or simply having a good time. That said, there are moments where they veer more towards the cynical end of the scale. Such as in the song "Californication" (which paints a VERY cynical portrait of Hollywood and its cultural influence).
Even by the standards of Black Metal, Deathspell Omega are an unusually cynical act, with most of their lyrics centred around a metaphysical view of why Humans Are Bastards. Their latest album, The Furnaces of Palingenesia turns their eyes to politics (and more specifically, to the resurgence of authoritarianism in contemporary society) and is just as pessimistic as ever; in fact, the album ends with the collapse of all of human civilisation, to the extent where there aren't even ruins to show that it ever existed. It should be noted, however, that this album is something of an aberration in their discography in that it indicates that the band does have ideals; they simply have no faith that humanity will or even can ever live up to them.
Panopticon manages to occupy both ends of the scale at once. A large portion of the band's catalogue deals with humanity's devastation of the environment, mistreatment of one another and of animals, and various other wrongdoing. However, many of the songs also express a hope that someday we will do better.
Invoked in "Fairytale of New York" by The Pogues with Kirsty Mac Coll, a duet between two lovers at opposite ends of the scale: he's at the idealistic end, she's at the cynical end.
hide is near the middle of the scale but leans cynical. His songs include dark lyrics about date rape such as "Genkai Haretsu", and angry protest songs such as "Doubt" and "Oblaat", along with themes of suicide. Despite this, he's not wholly cynical, as demonstrated by songs in the middle of the scale such as "Dice" and "Pink Spider", with his overarching messages being about pushing forward through pain and depression and Be Yourself.