Arduino mumble mic
We use [http://mumble.sourceforge.net/][Mumble] quite a lot at work.
However the level detection isn't optimum, meaning that typing creeps onto the channel etc.
Ergo most people switched to using PTT (push to talk).
However people often forget to push when they want to talk, and I personally hate headsets with microphones.
So I bought a CB mic or two, took them apart, and wired them up to an arduino to translate the switch on the mic to a USB key-press.