Songza is a site where you can, for free, look up and listen to entire songs when the mood strikes you. They have some neat tools, one of which allows you to send a song to a friend, one to embed a song on your site, one to link to a song, one to post a song to Twitter, etc. Good if you're looking to listen to, but not purchase, a song--or to listen to the whole thing and not just a sample before purchasing. I haven't delved into their collection too deeply, but I was able to find Madder Rose's "Swim", which is not available on iTunes--and unable to find the B-52s' "Dry County," which I had stuck in my mind today on my commute. A quick search on the song I most obsess over, Laura Branigan's "Gloria," also yielded live performances of "Don't Cry For Me, Argentina" and "Me & Bobby McGee" by Branigan.
Links to some of my favorite songs of the last year (in pop, at least):
"This Heart is a Stone" by Acid House Kings
"1969" by Montt Mardie
"Toxic" cover by Mark Ronson feat. Old Dirty Bastard
"Blue Motorbike" by Moto Boy
And an oldie to shake your coffee to this morning:
"Bust A Move" by Young MC