Any of Asus, XFX and EVGA are good cards. I have two Asus 9600GT Silents here in two separate machines without a single problem ever.
A 9600GT or 9800GT will be what you want, but not for £50 or lower. Cards even half-decent for gaming do cost a bit more.
Overall, however, you can get a gaming system for under £500 easy.
(Two example configurations: AM2 mobo + Athlon 64 X2 5000+ 65w or Asus P5Q + E8400. The E8400 is £80 or so more expensive with massive power.)
... really, if you can wait - E8400, 2x1gb Kingston ValueRAM 800mhz, Asus P5Q, Asus 9800GT, 500GiB Seagate Barracuda SATAII, case, 500w 80plus power, Samsung Superwritemaster. Enough power to play any game today well at an affordable price.
Or if you can't, Athlon 64 X2 5000+ 65w, AM2 mobo, same ram, hdd, dvd writer and most certainly a 500w 80plus power.