Your budget is going to place abit of a limit on your choice. If you can up it a wee bit to £91, Overclockers have 9700 Pros (this week only)click here
Before I upgraded to an Nvidia 6800GT, I had an FX5600 Ultra, which was OK and played Doom3 without problems, so I guess a 5700 wouldn't be too bad, although the LE versions are I beleive detuned standard 5700's. A friend of mine has a 5700LE and is happy (plays COD, GTA etc), although he is a casual gamer rather than and addict like me :).
You could check out the VGA charts: click here for some further ideas.