This is more expensive than the recent XPS deals posted on here, but it also includes a 22 inch LCD monitor so IMO it's a great price for a powerful machine.
Intel® Core 2 Quad-Core Q6600 processor (2.40GHz, 1066MHz, 8MB cache)
3072MB 667MHz (2x1024 + 2x512) Memory
750GB (7200rpm) Serial ATA Hard Drive with 16MB DataBurst cache
512MB nVidia® GeForce® 8800GT graphics card
16x DVD+/-RW & 16x DVD Drives
Logitech Cordless Desktop EX110
Dell 22" Black Wide Flat Panel (E228WFP)
Genuine Windows Vista® Home Premium - English
You get a total of £75 off in discounts - valid until April 23rd, plus free delivery. The price I posted includes V.A.T. and delivery.
E-Value code: UKBSDONL-D044010
Click the link to go to the deal then select the EX110 keyboard/mouse bundle, which actually lowers the price by £3 rather than adding £7 to it as the site implies. The discounts are applied once you've added the computer to your basket.