An Intel Atom D945GCLF mini ITX was reccomended to me, I believe it is all supported by plan9 and draws very little power. I was going to use one to replace a large noise server I have at home.
They also have a new dual core version though I think it has less useful I/O for my needs. http://www.tranquilpc-shop.co.uk/acatalog/Motherboards.html -Steve
