Here's some of what I've been using:
Songsterr for tabs on the Mac and iPad.
Garageband on the Mac (the last Mac update made it a really useable application with great features and results: bit of a Logic Pro-Lite) & iPad/iPhone, and there is free controller for the Mac version on the iPad called Logic Remote
Amplitude (there are a number of add ons [Hendrix/Slash/Marshall] and a good recorder) for iPad/iphone
Ampkit for iPad
Jamup (and Bias amp modeller) are probably the best sounding amp/effects simulator on the iPad/iphone
Fasttune HT6 is a good polyphonic tuner on the iPhone/iPad
I tried Riffstation and few similar products but didn't have great results... but that might just be me :smile: