The £200-£250 price range for graphics cards has been really exciting as of late with both the ATI HD 4890 and the nVidia GTX 275 providing oodles of performance for a great price. However, there's no denying it, £200+ is still a huge amount to spend on a graphics card - especially when you can get an entire games console for that sort of money. So, if you only occasionally use your PC for gaming, have a small monitor, or just generally are a bit strapped for cash, the price ceiling is more like £100. In which case a prime candidate for your money should be this new card from ATI.
The HD4770 is built around the RV740 GPU, which is the world's first graphics chip to be built on a 40nm process, whereas most other cards from both ATI and nVidia currently use a 55nm process. This smaller manufacturing process makes for smaller transistors, meaning more can be fit into the same size piece of silicon. In the case of the RV740 it has 826million in a piece of silicon only 143mm^2. In contrast, the RV770 (as used by the HD4870 and HD 4850) uses the 55nm process and contains 965million transistors. The resultant slab of silicon is 267mm^2 - quite some difference, I'm sure you'd agree.