Matt I've used these before to get my stuff: http://www.scan.co.uk/ http://www.overclockers.co.uk/ http://www.crucial.com/uk/ http://www.pcworld.co.uk/ Feel free to add to the list.
Hareng Got to know your prices and specs at these markets, they can work out dearer or be old unwanted stock. http://www.computermarkets.co.uk/ http://www.microdirect.co.uk/home.aspx Some good prices but not the latest specs stocked http://www.pcworld.co.uk/ http://www.cobra-computers.co.uk http://computers.ebay.co.uk/