What games are you planning on playing? Do you really care about framerate and graphics quality?
Your computer is good so far, can't really think of anything wrong with it. For a graphics card you may as well go with a GTX 650 or HD 7750. They deliver great performance for gaming at around £90 before prices start getting ridiculous. If you are more of an enthusiast and want to play Crysis 2 and Battlefield 3 at 60fps and 1080p as well as all the other games that are coming out next gen then get a GTX 660 or HD 7870 at around £180.
Also, if you want to upgrade to Ivy Bridge I'll recommend you a great CPU and mobo combo (possibly the same as mine) and I recommend getting a larger HDD and an SSD as a boot drive too. Apparently cheap CiT cases aren't too great either, I recommend getting a Casecom KM - 6788 (the same as mine) or a NZXT case if you want to go high end.
