Velocispider is nice. Not great, but nice. Its like Space Invaders with a different theme, you tilt your device to move back and forth and you fire automatically. Killing enemies will sometimes drop powerups and stuff. Its a tiny download and its worth having a peek at the pixel art, might be something you'll play when you have 5 minutes to spare, but thats probably it.
Shit, I do so much of this stuff I should start writing iOS reviews.