www.ebuyer.co.uk is probably one of the cheaper places (far cheaper than overclockers normally)
And strangly and I hate to say it www.comet.co.uk will be the cheapest for things like printers. due to thier price promise. Often low Web price and if couple with free delivery it even bettter.
Use www.pricerunner.co.uk www.pcindex.co.uk for price searching though
But I think the problem is 'Rebates' are not a big thing over here, or money off
But I do hope there are some people than are good at finding the coupons for some extra money off