I've seen a few threads about music and who's the best, so why not have a discussion of the best songwriters of all time? Keep this simply to pop/rock music, not jazz. I could name off a SLEW of jazz musicians, but I consider these people composers, not songwriters.
I'll start, in no particular order:
-Bob Dylan
-Bob Dylan
-Bob Dylan
-Benjamin Gibbard (Deathcab For Cutie, etc.)
-Bob Dylan
-Paul McCartney
-John Lennon (I don't even like the Beatles, but have a MASSIVE amount of respect)
-The collaborative effort of Incubus (post-2001)
-Stevie Wonder
-John Mayer (I know, I'm sorry, but I'm also very serious. His music is incredible, down to the simplest lyric or riff)
-Bob Dylan
-The collaborative effort of Fleetwood Mac
-The Jonas Brothers
-Benjamin Gibbard (Sorry, just reinforcing, and if you've never listened to Deathcab For Cutie, shame on you. You may hate the music, but his lyrics and melodies will rip at your soul no matter what).
-Tom Waits
-Just kidding about the Jonas Brothers
-Ben Folds Five
In my opinion, these are at the upper echelon, and all I can think of at the time. Feel free to flame, add to, or agree with this list, which is still in no particular order.