I do tend to think in terms of albums and artists, not songs, but as far as stuff you've never heard, David Wilcox is great if you like folk acoustic stuff. A few cuts off of his "Big Horizon" album have the highest play count on my Empeg. You can check out a few free songs from mp3.com:

http://artists.mp3s.com/artists/154/david_wilcox.html

Also of course is the oft mentioned "Moving Pictures" (album) from Rush, though most of these songs are well known. Still I run into an amazing number of people who've never heard it.