TC-11 is one of the earliest multi-touch music applications made for the iPad. It is available in a fully programmable version (for €29.99) and as a player, available for free but most useful with the preset pack for €9.99.
Thumb Jam (Sonosaurus LLV) – €10,99
NodeBeat: Playful Music – Gratis
Animoog Z (Moog Inc.) – Free – €17,99 für “Unlock Full App” – Diverse Erweiterungspacks