Mine has to be Gwen Stefani's What Are You Waiting For? I just love the song to death! Catchy as hell, a bit loony, and just refreshingly different from all the other generic pop songs that are almost always about love. Bleh.
Other songs that have been on continuous repeat on my player this year are:
Blood Brothers' Love Rhymes With Hideous Car Wreck
REM's Man on the Moon (started listening to it again after reading Andy Kaufman's biography - the song is about him)
REM's Everybody Hurts
Franz Ferdinand's Take Me Out
Killswitch Engage's Rose of Sharyn (Amazing lyrics)
So what's yours, let me know. Unless it's The Reason by Hoobastank then forget it. I'm kidding, i'm kidding.