Try
http://www.dinopc.com/. I got mine from there. When I bought it the site had a bug and if you chose a computer and specced it up completely, added it to shopping cart then hit the back button, it'd take you back to the selection page, still fully specced but with original standard price. Added that to cart, deleted the expensive specced up one and checked out

Didn't go ott too much as otherwise it'd be obvious, but I got about £100 worth of kit free

AMD Athlon II X4 635 AM3
Asus M4N68T mobo
4gb corsair 1600mhz RAM
500GB S-ATAII 3.0Gb/s
ATI Radeon HD 5770 1GB
700W EZCool Tornado PSU
The I stuck a creative x-fi sound card I had from my old system along with a few extra fans.
Like VW BUSH I'm able to play all the new games with the highest graphic and audio settings with no lag or frame rate issues. The only thing that's letting me down is the screen, the refresh rate isn't able to keep up with the graphics card and I'll get some uneven graphics unless vsync is on. I tried a mates HD sony screen and it was epicly good graphics.
Alienware is overpriced as feck. For the price of a decent alienware you'll get yourself the very best custom built PC available on the market today.
Scan.co.uk
Dinopc.com
overclockers.co.uk
^ They're the places to buy different bits and bobs. Buying a mobo and CPU bundle usually works out cheaper

Important to keep it clean too, both as an operating system (disk cleaner, reg cleaner, etc) and physically. Once a month or so I take the side panel off and using a car of compressed air, a small soft brush and a vacuum cleaner I'll clean out all the dust from every corner and from the fans. I use the small brush to carefully run it over the mobo to clean it out too. Be careful doing this though, because of it I buggered up my old system (it did need upgrading anyway). I tried lifting the CPU heatsink and the thermal paste was bonded solid and lifted up all the copper tracks under the CPU, rendering it completely useless.
Oh and upgrading the CPU fan is a must if you overclock it and want to keep it running cool. I've yet to do it though but I still haven't forgotten about it.
