The Chilledpc experience seems to differ from person to person. I've found their communication is terrible, but they have a whole load of niche stuff that cant be found elsewhere.
Watercoolinguk.co.uk is based in Manchester I think, so you might be able to pick stuff up.

Others:
Specialtech
Coolercases
overclock
scan.co.uk (does some stuff)
thecoolingshop