Heres a decent website to compare graphics cards in terms of fps when gaming.
http://www.notebookcheck.net/Compute...s.13849.0.html
Only thing I would add is dont worry about running games on the highest settings unless you have alot of $ to spend on a laptop.... Also, and I dont wanna sound patronising, but when Manchester says "get a laptop with the best discrete graphics card you can find' what that means is that you need to avoid 'on board' or 'integrated' graphics cards. Even if they claim to be gaming graphics cards they probably wont run much.