well XFX and eVGA make great cards... but if you want the highest performance, it would probably be the BFG Tech 7800gtx OC, the just slightly OCed it and sell it for more money, but you can OC any other card further than they did and save a little money...
get the eVGA with the huge black cooler on top, there's the KO edition, then a regular edition. get the regular edition because 9 times/10 they are easy to clock over 500MHz and it's not 150 dollars for the guarentee. http://www.newegg.com/Product/Produc...82E16814130254
Edit: Shoot, you're from the UK. Well thats the card and you can try and find it elsewhere.
I got the PNY 7800GTX 256Mb, now admitidly on first glance PNY is not really a brand that comes highly recommended but this is my second I had a 6800GT which I clocked to an ultra (now in my work pc ;-) ) and I have this running at 495Mhz x 1.35Ghz both run stable never above the 40 degree temp mark after endless hours of gaming and benchmarking which aint exactly poor performance if I volt modded it and I could probably push it a fair bit higher aswell.
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