Most of them I know of farbicate in China, but are based in the UK.
I use:
Spirit Circuits http://www.spiritcircuits.com/
Quick-Teck: http://quick-teck.co.uk/
Wrekin Circuits: http://www.wrekin-circuits.co.uk
and have had good results from them all.
Quick-teck are probably the cheapest, but Spirit Circuits have a very handy free prototyping service, called "Go Naked".