Hope you don't mind the blatant advert, but due to an office move, I got a 
lot of kit to get rid off!

Firstly:

16MB Ethernet Acorn NCs (actually Proton clones):
48MHz ARM 7500FE.
Run NetBSD like a dream once you set up your boot server.
Make good X terms!
Can run in 800x600x32k or 1024x768x256 (use shared memory, so higher modes 
make the machine run a little slower).
UK power supply, but not too choosy

45ukp + carriage

http://www.precedence.co.uk/products/clearance/ncfb.jpg

Secondly:

I've a number of CATS motherboards and systems (including some brand new 
ones!). Simtec are still selling this board for 199ukp + VAT 
http://www.simtec.co.uk/products/EB110ATX/

I can supply either bare boards or anything up to whole systems with 
disks, RAM, ethernet and video cards. I can even pre-install NetBSD for 
you!

Run NetBSD (since 1.3F) and Linux, plus others.

50ukp + carriage.

I can ship internationally, but obviously, this is more feasable for small 
items (I don't want to send ATX cases!).

-- 
Stephen