Animoog is a really cool synthesizer emulator for the iPad that simulates the electronics of the old analogue synths that ruled the 70s before digital came along and ruined everything. The interface is a little daunting but it comes will a bunch of useful presets, and the UI encourages exploration with lots of knobs to twiddle and hidden panels to discover.
The awful secret I have discovered is that if you make an interesting enough sound (which isn't hard to do) then any collection of notes sounds good. At the moment I am sitting on my pouch in the shade recreating the Blade Runner soundtrack by pressing random keys. That Vangelis was a terrible hack!