the Lenovo Y560 is what i play on. I play at Windowed 768x1366, no AA, General/Distance Drawing at Standard, Textures at Standard, and no Depth of Field or Ambient Occlusion. Its really light, but I advise buying a laptop cooler because this thing gets hot. You can find an i7/ATI5730 for $1200, and sometimes a discount. (I ended up paying $800 for mine)

Game rarely lags.

If you can, find a Refurbed Asus G73. Asus is pretty good when it comes to Refurbs, and the GPU is a beast. the only problem is that its huge. Again, you should probably get a cooler for this.

Don't get an Alienware.