[pdkl95]

I really like NightRadio's work. His main synthesizer, SunVox [1] is amazing. Innovative UI, very good analog-modeling, and a wide assortment of synthesis features. Oh, and it is available on almost any platform you want, most for free.

Also, I suggest checking out the NightRadio's other project, PixiVisor. [2] It converts an image (progressive scan) to audio and back again. This lets you, for example, see an image processed by a reverb effect, resonant LPF or whatever. It does things with the Fourier transform that I would have guessed were impossible.

[1] http://warmplace.ru/soft/sunvox/

[2] http://warmplace.ru/soft/pixivisor/

[bane]

I'd also recommend the Caustic softsynth, another very impressive Android/iOS/Windows tool. The Windows build is free.

http://www.singlecellsoftware.com/