I will try to make a few suggestions and back them up.
1) Build your own desktop. This will get you the absolute most performance for your money, but it requires that you are willing to buy the parts separately and then build the desktop. I have a build in my Newegg wishlist that costs $680 that will outperform any laptop/desktop you can buy in the same price range. Of course you have to add in $100-$200 for peripherals if they are needed.
2) laptops
http://www.newegg.com/Product/Product.aspx?Item=N82E16834115864
This one has a pretty decent DX11 gpu. With the latest patch, WoW can run significantly faster when a DX 11 card is used. It also has a quad core phenom II processor.
http://www.newegg.com/Product/Product.aspx?Item=N82E16834115860
This one also has a DX 11 gpu along with an i3 processor. The i3 is a better processor than most of the old core2duos and will give better battery life. There is really not any kind of difference between the i3's and i5's for your needs. As long as you have a dedicated video card, you should be able to run WoW fine.
If you want to spend less you could go with an IntelHD laptop. It will run WoW, just not great. You should be able to run on low-medium settings just fine. The newer onboard graphics are quite potent when compared with some of the others.
3) desktops
http://www.newegg.com/Product/Product.aspx?Item=N82E16883227274
Faster than all of the laptops and will run on Ultra settings just fine, but I don't particularly think highly of iBuyPower.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883220051
Faster processor than the other desktop, but a slower video card. Ultra settings would again be a breeze.
Both of these desktops are sold out on Newegg though. But if you find a similary spec'ed/priced desktop elsewhere then you can't go wrong.
My first suggestion is a personal favorite. I recently took the dive and built my own computer, and it was worth every minute of googling I had to do. It was also fun, and I now have a computer that breezes through every game I throw at it. But if all you want to play is WoW, it may not be worth your time.