Here is a trick by Robert K using the Ableton Live Simpler Instrument to manually/randomly change the playback of a sample resulting in something very similar to granular synthesis.
Generate audio in your browser by certain rules with the WoframTones Generator. You can download results in several audio fromats and as well as MIDI files.
16,000 BBC Sound Effects are made available by the BBC in WAV format to download for use under the terms of the RemArc Licence.
Zombi-Fights-Shark compiled 60000 presets from Yamaha DX sysex files for Native Instruments FM8 VST synth. You can download these for free (Donation possible).
This is a nice MIDI controller from Artifon. Not cheap though, 600+. Features:
Play guitar, bass, synth, violin, drum pads, and more, on a revolutionary MIDI controller
TIME Magazine “Best Invention of the Year,” #1 Instrument on Kickstarter, PCMag Editors’ Choice
The first fretted and fretless digital string instrument; low-latency, pressure-sensitive playing
Ultra Portable: Lightweight and 6-Hour Battery Life; USB & Lightning Cable iOS and Mac Connectivity
2 Stereo Speakers & Headphone Jack for creating on your own, or jamming with friends
Free dynamic equalizer from Tokyio Dawn.
Frequency selective compression
One of the best in their field, Project Sam offer free orchestral instruments (Registration needed)