[BobM]

This list is very subjective. I've listed mine but I totally left out classical, prog and jazz. These are mostly well known people that I tend to enjoy. You list will probably be very different. No particular order within a tier.

Tier 1
Lennon/McCartney - they were never as good apart as they were together so I'm counting them as one
Paul Simon
Elton John
Billy Joel
James Taylor

Tier 2
Steven Stills
Don Henley
Bruce Springsteen
Cat Stevens
Joni Mitchell

Tier 3
Sting
John Fogerty
Kenny Loggins
Pete Townsend
Kevin Gilbert

Tier 4
Roger Waters
Billy Gibbons
Donald Fagen
Stevie Wonder
Van Morrison

[Photon46]

In alphabetical order, some of my top writers:

Bryan Ferry
Neil Finn
Lisa Gerrard / Brendan Perry ( Dead Can Dance )  As you mentioned with Lennon / McCartney, I prefer their strengths together as opposed to individually.
Rickie Lee Jones
James McMurtry
Christine McVie
Joni Mitchell
Cat Power
Patti Smith
Tom Waits

[saggy]

wow - you guys need to hear about this new dude making the rounds....his name is Dylan or something.