Exquisite choice, Biffy! I found one lyrics site that claims 176,000 lyrics. I figured that pretty much covers Thompson’s stuff but I thought they claimed songs by other writers, too. 
I heard him interviewed once and he told how he considers songwriting his job to the point that he rents an office and treats songwriting as a 9-5 job.
This morning I downloaded and listened to “Barrett’s Privateers” and “Fogarty’s Cove”. And, no offense, unless “Harris and the Mare” is radically different from those songs, I’ll not be interested. His constant vibrato drove me up the wall.
Well, I wasn’t really being serious, as I’m not familiar with much of his output myself. I was just snarking about the implied attitude of “I’ve never heard of him, therefore he can’t be anyone significant.”
I’d second Richard Thompson and add Nick Drake. I like Leonard Cohen, but as has been pointed out, he’s more about words than music (or even singing). And I know Nick Drake’s output is miniscule (and not necessarily “intellectual” like many mentioned), but he’s pretty damned cool.
You read much deeper into my superficial comment then. 
Tom Lehrer
Mockingbird beat me to it. Tom Lehrer, definitely.
Jeff Buckley, anyone?
I second that vote.
Well, isn’t every week on the SDMB National Brotherhood Week?
GD: Pete Seeger - Intelligent, been around a while and has a slight leftward tilt.
MPSIMS: Paul Simon - Fun, diverse and always entertaining.
IMHO: - David Buskin - Opinionated, popular and sometimes repetitive
The Pit: David Peel - Gritty, abrasive, anti-establishment and angry.
Cafe Society: Bob Dylan - Most recognized in music.
On second thought, he hasn’t written any comic book, Star Wars, LOTR, Star Trek or Harry Potter-themed songs - so there may be a better choice out there.
I agree on all three points.
Nah, more like Masochism Tango.
**Elvis Costello ** - what a mean sense of humor (perfect)
Tom Waits will do just fine for me too
I’m very fond of Elliott Smith too, but my wag is that a guy who offed himself by stabbing himself in the chest in a fit of pique might not capture the imagination of a lot of dopers.