BeBot is a lot of fun, it has a silly robot that "sings" while you play. but forget about that its a great and playable instrument.
the synth is incredibly simple but you can express the filter or pulse width on the touch screen.
it can be played like a theramin, or with steps (and you can program the scale) and you can set it to glide or snap to the closest pitch of your scale.
this afternoon i hooked it up to all the guitar effects in my roland VG-99 and played along with a tune i was "working" on. once you get some guitar effects and amp sims on there its pretty convincing as a guitar.
you can go completely nuts like Eddie Van Halen or Steve Hillage

im probably going to make a little youtube of it tomorrow.
i really dont think the programmer knew he was creating a monster, probably just thought it was a little cute fun thing.
best $2 i spent in ages.
*yes i know theres that cool OSC control thing but i dont have a MAC so i cant use it

*yes theres that noise synth thing its a pain to use and can crash my ipod
*maracas and stuff like that i grab them all but they are one trick ponies.