Osu! for iOS
If you have played Osu!, Ouendan, or Elite Beat Agents, this is basically that kind of game. It also uses your own music on your ipod/iphone/ipad. It is quite difficult to learn if you have never played rhythm games before. (I started on hard since i was used to it)
DragonFire92x about
The Real Beat - Rhythm Game, v1.03