As others have said, go for a 7900GT, 256Mb memory, for around £250.00.
I thought ATI had the leading edge for a while and I championed their cards. But I think since after they produced the 9800GT AGP card, they kinda lost the plot.
Their drivers were good a couple of years ago, but now they're dependant on Microsoft Windows' NET Framework software to run efficiently. Not much good if you happen to be running a Linux setup. A damn shame, as ATI were doing good for a while there.
At this moment, I'd only recommend Nvidia, though things do change. In fact, those who constantly, blindly, support one make are probably deluding themselves and being foolish but that's another subject
Also spotted this at Overclockers.co.uk, not out right now but should be soon. For £329.00 looks like a good buy:
Gainward BLISS Geforce 7900 GT "Goes Like Hell" 512MB GDDR3 TV-Out/Dual DVI (PCI-Express) - Retail (GX-034-GW)
The new flagship NVIDIA® SLI™-Ready GeForce® 7900 graphics processing units (GPUs) are designed for extreme HD gaming and deliver ultra-realistic gaming experiences and unparalleled image quality at resolutions of up to 2560x1600. Need a break from gaming? The GeForce 7900 GPU also delivers smooth, high-definition video playback and crisp picture quality thanks to its advanced NVIDIA® PureVideo™ technology. If you are searching for an extreme HD gaming and video experience on the PC, look no further than a GeForce 7900 GPU.
- GeForce 7900 GT Core running at 580MHz+ (Final release speeds will be quicker)
- 512MB GDDR3 Extreme Memory running at 1650MHz+ (Final release speeds will be quicker)
- 24 Pixel Pipelines
- Designed For Extreme HD Gaming – Delivering Ultra Realistic Gaming Experiences
- Nvidia Pure Video Technology – Delivering high definition video playback supporting H.264 and WMV9
- Dedicated Video processors free the GPU Shaders to run 3D applications – Letting the GPU do what it does best
- Built for Windows Vista – The next generation operating system
- Dual link DVI support
- SLI ready – Delivering upto 2x the performance
- Shader Model 3.0 Support
- True High Dynamic Range Rendering Support – Based on Open EXR technology
Arriving end of April 2006
Price: £279.95 (£328.94 Including VAT at 17.5%)