Dell are good. They only sell online but if you look in most daly papers or some magazines they do loads of deals.
Dont buy the first one you see on the Dell web site.
Try selecting various options on the web site to get the best price. Look at the various deals and see what special offers are available.
Often they offer double memory, or larger hard disk, or bigger monitor on certain models.
I bought a good Dell PC a few weeks ago for my son with 1Gb of memory, 80Gb hard drive, 17" flat panel monitor, for about 440 pounds including delivery.