AudioMulch 2.2 is just around the corner. It adds MIDI output contraptions. This makes plugins capable of processing or sending MIDI much more interesting to use in AudioMulch, since you will be able to send MIDI from plugins to outboard MIDI hardware.
We've put together a list of MIDI processing and generating plugins for Mac below. Please let us know about any others and we'll update the list. There's also a related list of Windows plugins here.
[Last update: July 20]
Piz pizmidi collection - small useful MIDI processing plugins. Currently free and highly recommended.
Piz MIDI plugins - additional MIDI plugins from Insert Piz Here
Numerology (Mac only) - Modular music sequencing, analog sequencer style step-sequencing and modulation.
Eckel - Euclidian sequencer
Cableguys MidiShaper - flexible LFOs and envelopes