I actually just got batteries for my VMU!
Man, there are actually quite a few good vmu mini games. Chao Adventure, Powerstone Mini, Sega GT, Football are all really cool vmu game but, my favorite has to be the Soul Calibur game. It is the only game the attempted voice sampling to my knowledge. Has great animation and some fun games to it. I mean where else can you shoot Soul Calibur characters out of a cannon? I wasted a lot of batteries with this game. If anyone hasn't played this one yet go do it!
(Don't forget to enable the BG music in options)