Reader Nuno pointed out that Meteor Multitrack just got a minor update, increasing the polyphony of the drum parts.
I think it is really great that this "Recorder" app includes so many virtual instruments as part of the deal! I haven't played with it yet though. Leave a comment, if you've played with it, and let us know how it is.
Here is a demo from Marcus over at MusicApps.com.br, playing with the virtual instruments. He starts off with the drums being triggered by a MIDI keyboard.