I've seen/tried a couple guitar apps, tried a piano one and wondered what sort of luck the musically inclined are having with the various android music apps, and if they find them limited or not.
After having watched this video of iApps I decided that all I want for Christmas are some better Android music instruments. If you've find some, feel free to add to the list
Ones I've tried:
gStrings - a tuner app
guitar solo light
Musical Lite with piano