Let me start by saying that the problem with using a laptop for gaming is that the more power you put into it, the less portable it becomes, and you can't upgrade the system like you could with a tower. That being said, I can understand the need for someone who can only afford one machine.
I'll describe what I would personally be looking for in a gaming laptop if I were in the market for one.
Ram: 8gb minimum. Ram is cheap enough that you could buy 16gb for between $100 and $130. This is one of the only components you can actually upgrade yourself in most laptops.
CPU: Quad core i5 or i7, 2.4ghz and up will cover pretty much anything you need to do.
HDD: The hard drive speed could affect loading times in certain situations, so it actually
can make a difference, but isn't commonly considered. A solid state drive (SSD) offers the quickest seek times, but is extremely expensive per GB when compared with platter drives. However, they do make hybrid drives now that offer most of the advantages of an SSD along with the size of a standard hard drive. Not really a game-changer but something to think about. Can vastly improve boot times.
GPU: The mobile graphics card. This is going to be the biggest issue and none of them are going to stack up against a standard desktop GPU. On the plus side, WoW isn't that demanding of a game.
You can check
this site for some mobile GPU benchmarks (SLI and Crossfire mean two graphics cards are being used), but it looks like the GeForce GTX 580M and 675M are pretty good cards. Do NOT get tricked by the model numbers, they're utterly meaningless, use benchmarks to find the card you want.
iBuyPower might offer the best bang for your buck, followed by Asus and then maybe Alienware although I don't think they're what they were before being bought by Dell.
You're looking at between $1000 for a lower end laptop "gaming" rig and $2000 on the high end.