MiniSynth Pro has been updated with 42 news presets "created by professionals", and the price has been dropped in half to $5!
I don't know much about this synth, but it has lots of Pro features including (Virtual)MIDI, recording, and AudioCopy. It also has a lot of modulation options, or as their iTunes description puts it:
It features our special dynamic waveform selection algorithm, individually parameterized voice processing, and carefully selected waveforms driving its dual interactive oscillators and its five-destination LFO.
I have no idea what the fuck that means, but it sounds awesome! Maybe someone else can explain this in the comments.
Here's a surreal jam the developer, Yonac, put together showing off the MIDI and modulations.