Chow offer great cross platform plugins for free.
Blog Archives
Animoog Z Presets
Free presets for the free (plus IAPs) iOS synth Animoog Z from Expanding Sound.
Tape Cassette 2
Tape Cassette 2 is an audio plugin that emulates the warmth, noise and character of old tape cassettes. More info and download.
Electronicsounds
Get lots of free samples/patchs for iOS apps or as Wav files from Electronicsounds (Donations possible).