If you live in Scotland, we can recommend the following shops from personal experience
Ideal Computing, Edinburgh. Good systems at competitive prices, my favourite local PC shop in Edinburgh.
SortMyPC, Colinton, Edinburgh. Competitive and knowledgeable helpful staff, free parking nearby too. I use them and would highly recommend them.
Great for components, bargain systems and hard to find stuff.
Dell UK - Desktops. Have used them extensively in various offices and they have proven reliable and good value for money.
You could also try Tesco direct:
Back to Silicon Glen, Scotland