Personally i'd look up the kinda of specifications you're looking for and then do some searching on eBay. I've just picked up this one
http://www.ebay.co.uk/itm/281314865924?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649Seems like i've got a pretty good deal, got it for less that it was listed for and couldn't find anything like this for anywhere near this price going straight to a big name online retailer.
Cliffs on mine:
OS: Windows 8.1 Home Premium
Processor: Intel i7 3.4GHz
Memory: Kingston Hyper 24GB
Graphics Card: Nvidia GTX 765M 2GB
Hard Drive #1: Western Digital 750GB
Hard Drive #2: Kingston Hyper X 480GB SSD
Optical Drve: Blu-Ray
Cost: £1k