I bought a Micromys from amigakit (
http://amigakit.leamancomputing.com/...oducts_id=1092) since I had a few ps/2 mice sitting there collecting dust.
There is also the Rys mk2 adapter for USB mice and joysticks (it has a minimal USB stack - enough for mouse and joystick) (
http://amigakit.leamancomputing.com/...oducts_id=1272)