Google Translate: Freaky cool. Does an amazing job. Will speak and write the translation.
Wolfram Alpha: Type in C# harmonc minor scale and the scale comes up. Great resource for just getting the facts. Let alone it is an amazing algebra/calculus engine.
VoiceJam: We haven't quite figured out how to use this, but it is a very cool loop generator. Watch the video.
iGuitarFree: pretty cool and good sounding app. Would like a quality guitar chord generator. Ideas?
Trio: allows three people to play on same iPad. Bass, piano, and drums.
#1 Thing we use on iPad: piano.
#2 Thing we use on iPad: youtube
#3 Thing we use on iPad: internet/musictheory.net
I have a compilation list on 2/14 entry. Check it out.