There are a couple, Midi Performer, I think it's called, is a very good app (it's also about $50 Oz as well)...

I am awaiting Music Reader, or Unreal Book to get the MIDI implementation setup though, as for my needs (reading of charts linked to Korg Songbook setup midis) either of those two apps is plenty.

But the list of apps supporting the Midi Mobiliser is growing http://line6.com/midimobilizer/more_apps.html

Dennis