What is the opinion of Reddit about the
IOGEAR 4-Port HDMI Multimedia KVM Switch with Audio, USB 2.0 Hub and HDMI KVM w/Full Set of Cables, (GCS1794 TAA Compliant)?

Yeah, there should be a HDMI KVM switch out there in the market. Its exactly what you need.

Just had a quick look on amazon, this looks alright: http://www.amazon.com/IOGEAR-4-Port-Multimedia-Switch-GCS1794/dp/B001V9LQ52/ref=sr_1_1?ie=UTF8&qid=1324127916&sr=8-1

Edit: Looks like Bastakks beat me too it, and by price too!

Heres one. Does 4 machines, is probably more money than you want.

This KVM should do exactly what you need.

Edit: Revised link to a 3.5mm version.