my mate has a 303 emulator on his
(i hate myself for not getting an iphone, but Im glad i stuck to my anti-apple guns)
theres some pretty cool sequencer apps i've seen on youtube as well, would be a fun way to spend a lunch break tapping out some beats
might get a touch just so i don't feel left out, i thought you HAD to have itunes to get it working but i read on here winamp does the job (itunes is the devil)