Either Bacteria, Re: Your Brains, Baby Got Back, Shop Vac, Bills, Bills, Bills, Mr. Fancy Pants and Soft Rocked By Me.
I know there are others, but these are just the first ones I got from my Winamp list. All his songs are just...good.
I think Shop Vac is probably my most favourite (or at the very least a strong contender). Those clap-like sounds in the background always make me tap along to this song, and the song overall is just catchy and great.
And just as a bonus, my least favourite Coulton song, no doubt, is Rock And Roll Boy. It's just...retarded. I hate it. But it's, like, the only one.