Pay a visit to
ebuyer.co.uk and check out the Laptops available there. You can generally pick up something for £500 or so.
I would avoid Dell unless you are quite good technically as when you have a problem then you will discover Dell's BIG problem - tech support. They will try endlessly to fix it over the phone and only when they have exhausted all avenues will they consider a visit from a tech, timing to suit them of course. The kit is generally OK and I would buy it myself but be warned.
When looking for brands I would look for the one with the best warranty as laptop repairs can prove very costly. I was recently parted with £300 quid for a mobo which I worked on myself.
HP/Compaq, Tosh, Sony and Samsung are all models I have used recently and are all favourable.
Good luck and let us know what you get.
Quick Edit: - If you are feeling flush try here that is an extraordinarily well priced / specced machine for the money (bit sad looking here but they sometimes sell some damn good kit)