I would recommend the Asus G1 as a moderate to high end gaming laptop it was designed specifically for gaming, but it is a little out of your budget. So here is another Asus in your budget range. I have done enough research to have found out that users give the best reviews for gaming with there laptops go to Asus brand.
Dell has kinda gone crappy over the past few years although recently they have begun to clean up their act. They can also be rather expensive.
Why exactly do you want a laptop over a desktop? Are you completely sure you want to give up gaming quality for compactability? Furthermore, do you do any sort of graphic or web design?