Have a look on click here. I would recommend CUBE 247 as their customer service is excellent and their PC's are top notch they have gaming PC's on their site ,look at the reviews on PC Advisors web site they always get top marks in the Workbench tests, fair enough they are not the cheapest but they only use top quality parts and like anything in life you get what you pay for, also if you have any problems with them you can telephone them up and speak to someone who can help, I have found when I ring them that they are very very knowlegable. I have a friend who has a Dell PC and he says that their customer service stinks, he has told me that the call centre that you get through to is in India, my friend says its like banging your head against a wall trying to get any sense/help out of them. He also said he would not buy another Dell PC, as in his experience he says they are not the best or the most reliable PC by far.
Don't know where you live - I'm out in the sticks a bit but still have a good assortment of small local companies that service and build pcs. Pick a recommended one where you can sit down with someone who knows what they're talking about and will listen to what you want - if the final spec seems good get a quote. The advantage is if things go wrong you can visit them and get advice face to face ( without having to go to India!)