RandARP is a free VST plugin arpeggiator with many randomization features, allowing incoming notes or chords to be manipulated in various rhythmic ways.
Random Riff Generator is a midi tool by Mario Nieto that generates sequences for you. This is the free version.
This is crazy. Loligo is an experimental audio tool that generates sound from image data. Watch the vid and download here.
Spatium is a set of free, open source and modular software tools for sound spatialization. Download here.