Just updated today on XDA:
http://forum.xda-developers.com/showthread.php?t=477002
Sheon's Omniano. It's an 88-note keyboard application that actually sounds like a piano. And it's just one version away from becoming a full band. This latest build lets you play polyphonic chords: only 2 notes at a time, but it sounds full and sorta like a real chord. That's supposed to be impossible on a Touch Pro but it works as advertised on mine.
I've been following this app from the beginning and it has come a long way. Like Iperov's PDA guitar, it's still a work in progress but it's progressing really well. I'm an occasionally professional musician and I've wanted a pocket-sized piano for a long time.
This easily gets a couple of thumbs up.