I want something fun and upbeat. As much of a douchebag Chris Brown is, I really really really REALLY love Forever. Future Hub wants Colbie Callait I Do (cute, but I'm a bit more quirky than that).
Another one I like a LOT is Signed Sealed Delivered by Stevie Wonder, especially since I grew up listening to a lot of music like that. He tends to be more traditional.
Of course, our wedding is a year away and new music comes out all the time but what are you using or what have you used?