Lou Reed
John Hiatt
Leonard Cohen
Tom Waits
But…on the other hand, while they, and a lot of the people mentioned (I say a lot 'cause i really don’t care for Sondhiem. or Sting. or Billy Joel) have all the great lines, let us remember that lyrics are not meant to be read but to be heard. Like for example I was just this minute listening to Syd Barrett “No Man’s land” and he has this line “we under all we awful awful crawl”. Doesn’t read like much, but it sounds…haunting.
in a similar spirit let us not forget “a-whomp-bomp-a-loo-bomp-a-wamp-bam-boom” and “gabba-gabba-hey”
I would suggest to all serious (and even not serious) students of song lyrics they pick up a copy of “Sondheim & Co.” by Craig Zadan and read chapter 21 on Songwriting.
Those ten pages will give you a new appreciation for the craft of lyric writing in general – and theater songwriting in particular. Sondheim crafts a song like an architect designs a building. He is always mindful of a song’s pacing, structure, intent and (here’s where most other theater writers fall short…) context. His songs are never a slapdash of amorphous emotions and sort-of rhymes.
I have other favorites, many of which are mentioned above: Billy Joel, Fred Ebb, Frank Loesser, Johnny Mercer, James Taylor, Craig Carnelia (betcha don’t know who he is), and Irving Berlin.
But when it comes to, Who is the master at lyrics? It’s Steve Sonhdheim. Only Sondheim.
I’m talking Rock here, not like there’s any OTHER kind of music worth considering ;). Just my opinion, but I’m not much into top-heavy, pretentious lyrics propped-up by slim-to-none music. If you wanna do poetry do poetry. And I’m too damn busy for lyrics that are just strung-together cliches about love. 
Hence these are great:
Pete Townshend (The Who), definitely.
Ray Davies (The Kinks).
Frank Zappa was a brilliant lyricist but since he did satire no one takes him seriously.
Honorable mention: Jello Biafra (Dead Kennedys) and the guy(s) who did early Big Country albums, they were superb lyrically.
betenoir: Syd Barrett? You think he’s better than Waters/Gilmour? Gotta love “the papers hold their folded faces to the floor, and everyday the paperboy brings more.”
John Fogerty (Creedence Clearwater Revival) ?
Walter Becker and Donald Fagen,
hands down, no question about it.
Gordon Lightfoot.
Nothing better than an extremely talented songwriter who sings his own songs. Who else but the writer knows what he REALLY meant when he wrote the song?
Check out “The Last Time I Saw Her Face”, and–well, I could go on but I won’t.
And no, I am not Canadian.
Scotti
Cole Porter.
Wickedly funny, astute, touching, urbane, romantic, unforgettable.
And they rhyme good, too!
Definitely Becker & Fagen…
And Paul Simon----I often wondered if Art Garfunkel was jealous of Paul’s songwriting ability…Paul has had staying power in his career because he can write music–but Garfunkel has the voice of an angel…sigh.
Ani Difranco is by far my favorite lyricist. That woman is amazing.
Broadway shows have produced the best lyricists by far:
Cole Porter definitely.
Stephen Sondheim is a great lyricist, but unfortunately, only a so-so songwriter – by far the weakest of anyone on this list (or their partner).
Ira Gershwin
Al Dubin (Listen to “Honeymoon Hotel” or “Shuffle Off to Buffalo”)
Frank Loesser
Rock songwriters tend to lag behind. A few of the better ones:
Billy Joel (I never can recognize his voice, but when I hear a new song by him, I alway find myself thinking, “Good lyrics.”)
Keith Reid (Procol Harum)
John Lennon (at times)
Interesting coincidence: I saw Jello today at a convention in NYC. The guy is seriously cool.
I know you all are going to laugh at me, but I have to mention Barry Manilow. He may be on the down side of boring much of the time, but the man wrote a whole lot of really good songs.
This has got to be the first time in internet history where Barry Manilow and Jello Biafra have been complimented in the same post on any message board ever.
What about Howard Ashman?
He wrote the lyrics for several movie musicals.
Little Shop of Horrors
The Little Mermaid
Beauty and the Beast
Aladdin (about half of the songs)
Well since the “one artist per reply, if you would” rule has apparently been tossed out, I’ll have to second the Ani Difranco nomination and raise you Paul Westerberg from the Replacements.
Few artists can turn a phrase so masterfully as these two.
My top 3:
Neil Peart (come on, what do you expect?)
Paul Westerberg
Tori Amos
Gammu, but that’s not exactly what I meant. I’m not saying Syd had any great lines. If I was talking about lines I could drop into casual coversation:
“When they said repent…I wondered what they meant.”-Leonard Cohen
or useful bits of practical wisdom:
“Never trust a man in a blue trench coat. Never drive a car when your dead.” -Tom Waits
I would have stuck to my first two choices.
but I’m talking about a different criteria. Like something that’s stupid except in that song, sung that way.
So…best rock lyricist-Iggy Pop
“No fun to hang around. Feeling that same old way. No fun to hang around. Freaked out…for another day.”
Jimmie Rodgers
Hank Williams
Bob Nolan
Harlan Howard
Cindy Walker
Merle Travis
Willie Nelson
Bob Wills
Roger Miller
Since Mr. Carmichael, Berlin, Mercer, & Dubin have been mentioned (though not by me, since I still think Cole & Ira are the absolute tops), we cannot neglect Lorenz Hart, Richard Rodgers’ best musical collaborator and another one of the great lyricists.
I’ve always thought of Art Garfunkel not so much as of a person, but as a musical instrument:
Paul Simon - electric guiter, acustic guitar, tambourine, garfunkel.
By the way, you’ve forgotten Suzanne Vega. She can write with the best of 'em.