The Baby is ace; I also really like Share it With Me (both versions), Love Addict, Lose Urself, their cover of My Favorite Things, Whatcha Gonna Do With It, and Master of Disguise.
Are songs by other people okay? If so, here are a few:
Heatwave, Boyfriend, Q&A - Alphabeat
Life is Like a Boat, Romantic, Tiny Tiny Melody - Rie Fu
Gee, Into the New World, Tell Me Your Wish (Genie) - Girl's Generation (SNSD)
Ring Frie, Was Ist Das, Beweg Dein Arsch - LaFee
Leuchtturm, Mach Die Augen Auf, Willst Du Mit Mir Ghen - Nena
That's it for now... c=