I think Novatech (
www.novatech.co.uk) has already been mentioned, very good all round really, although they are going down hill slowly in my opinion.
Another favorite of mine is OverClockers UK (
www.overclockers.co.uk) not mentioned yet, they are quite good value and perfect for high end or high quality hardware, they only put that best on their site as far as I can see and have good support and forums.