For UK
Asus GeForce GTX 560Ti DirectCU II 1024MB GDDR5 PCI-Express Graphics Card []
there is also an MSI version with a slightly better clock and a better cooler for 173.
GTX 560 ti.. 161 GBP (available till 7th dec, new options every week.. have a look at their specials if not buying before then)
You will get a 560ti or a 5870 for that price (560 is my choice)
PSU, what is the rest of your machine's spec's, what is your current PSU?
I would suggest getting a better monitor in the near future if you can.. the 560 will be able to perform REALLY well at that res (at 1920x1080 it is still very good, if being a lil stretched on some titles with all eye-candy turned up)
XFX Pro 750W Core Edition '80 Plus Bronze' Power Supply 79 GBP. also in the "this week only section..
You may not need a new PSU, please say what other parts your running so that we can advise you on it properly.
You may be able to get a new monitor instead of a PSU if you have something that is sufficient, eg: 21.5" 1920x1080 benq for 119 GBP.
Fill us in on your other specs and we can suggest best options for your buget.