Pretty much the entire Quadrophenia album by The Who.
"You’re a loser, an abomination in the eyes of any sensible man.
And you’re a blind alley cruiser, always headed down a losin’ street
dreamin’ that you’re sceamin’ at fate
You’re a dead end dead beat no where mister
with a kisser like a Mississippi alligator sister"
the climax song to the movie Shock Treatment
Sitting on a park bench
eyeing ittle girls with bad intent.
Snot running down his nose
greasy fingers smearing shabby clothes.
Drying in the cold sun
Watching as the frilly panties run.
Feeling like a dead duck
spitting out pieces of his broken luck. – “Jethro Tull,” Aqualung
Actually,** At Seventeen** is a Janis Ian song.
Leonard Cohen has written about losers once or twice. In The Stranger Song, he writes:
It’s true that all the men you knew
Were losers who said they were through
And giving up the holy game of poker.
I know it’s hard to hold the hand of anyone
Who is reaching for the sky just to surrender.
In Last Year’s Man he tells us:
That everything would happen
If he only gave the word
And oh, the rain falls down, amen
On the works of last year’s man.
Ian Tyson, in 4 Strong Winds sings about a man who decides not to invite his woman out to Alberta to join him while he works at a job he’s not even gotten yet. He tells her:
But by then it would be winter
Not much for you to do
And the wind sure blows hard a way out there.
Then there’s also the narrarator of **Just Like tom Thumb’s Blues ** by Bob Dylan who is lost in the rain in Juarez during Easter (and then things go really bad for him.)
Or the narratoe of the song **Easy Times ** sung by Judy Collins who sings:
Easy times come hard for me…
Tell me how you spend your time
Here there’s nothing much to do
And the nights, they seem to last forever.
And the summer’s been so long
I was here and you were gone
Been that way as long as I remember.
Or the narrator of a song by the Cowboy Junkies who says:
Because cheap is just the way I feel.
“Young man sitting in an old man’s bar
waiting for his turn to die”
That my friends, is a loser.
Morcheeba’s Everybody Loves a Loser is kind of ambiguous but it IS about a loser 
It’s really a backhanded compliment to say: “I think you’ll find everybody loves a loser. So you’ll be fine, you won’t be lonely long.” Great sound to the song too.
OK, the posts bring another to mind…“Fool in the Rain” (if you have to ask who this one is by, check out now).
Locomotive Breath by Jethro Tull.
He’s not just a loser, but “the all time loser”
Springsteen’s “Glory Days” fits in here.
The Smiths - “How Soon is Now?”
Geez, I can remember when half the people I knew were Deadheads. Ummm, maybe I shouldn’t admit that.
Loser, by the Grateful Dead
If I had a gun for every ace I have drawn,
I could arm a town the size of Abilene
Don’t you push me baby, beause I’m moanin’ low
And you know I’m only in it for the gold
All that I am asking for is ten gold dollars
And I could pay you back with one good hand
You can look around about the wide world over
And you’ll never find another honest man.
Last fair deal in the country,Sweet Suzie,
Last fair deal in the town
Put your gold money where your love is baby,
Before you let my deal go down
are just a few lyrics, the guy gets more pathetic
Loads of Springsteen songs do. “Born in the USA” and “Johnny 99,” among others.
And a host of country songs. How about Johnny Cash’s “Folsom Prison Blues,” or Merle Haggard’s “Mama Tried,” both songs about men with nothing to look forward to except a lifetime in prison.
Margaritaville by Jimmy Buffett is about a loser, although the only thing in the song that’s explicitly lost is his shaker of salt.
WHOOP! I’m not the only Doper who’s seen Shock Treatment! 
That song gets bonus points, because it’s about TWO losers, though one is admittedly far more sucessful a loser than the other. Actually, a number of songs from that movie are about people being losers (mostly the ones centering on Brad)
Would the ultimate loser song be *Green Green Grass of Home * narrated from the point of view of watching everyong gather for his funeral?
Or how about Townes Van Zandt’s Tecumseh Valley?
Ben Folds Five had a “rarity” called “The Secret Life of Morgan Davis” which was their own version of the Walter Mitty story.
I would think most Belle & Sebastian songs are about losers. Or maybe that’s loners.
Scrub, by TLC, about their lack of desire to be around said losers.
How about Song For The Dumped from Ben Folds Five? 
Joni Mitchell’s loser song would be… wow most of them.
Big Yellow Taxi You don’t what you got til its gone.
- You Turn me on, I’m a Radio* You don’t like weak women, you get bored so quick, and you don’t like strong women, cause they’re hip to your tricks…
Cactus Tree …her heart is full and hollow like a cactus tree
*Cold Blue Steel and Sweet Fire * (from her own drug days)
Woman of Heart and Mind …drive your bargains win your metals fuck your strangers, don’t it leave you on the empty side?
People’s parties…and me in my frightened silence, thinkin’ I don’t understand
The Last time I saw Richard He sits at home most nights with the TV on and all the house lights left up bright.
Love or Money “Is one the moon, dear clown, tied to a string for me?” he tried but he could not get it down. For truth or mystery He tried but he could not get it down for love or money.
There are more. Those are from memory.
*Lather * by Jefferson Airplane …and I should have told him, no, you’re not old, and I should have let him go on…smiling.
I’m surprised nobody’s mentioned anything by Green Day yet. I mean, c’mon, this thread was made for them.