The HP DV 4,5 are pretty good laptops. Cheaper than the XPS and besides being very well specd they also look good.
For Asus check out the "F83SE". 512mb ati radeon 4570 graphics , 500GB HDD , 4GB ram and it comes with Windows 7 Home Premium. 14.1" screen. It also looks pretty neat. Brushed aluminum look.
I wouldn't go with Sony , nothing special.
Alienware laptops are great machines but really bulky and heavy as well.
Just to broaden your horizon: I even saw a Compaq CQ 61 which is a dam good deal. Forgot the exact model number but it had a 15.6" screen , 512mb video card (either nvidia or ati). Not 100% sure about the ram and hdd either but it was around 60k.
Don't just buy one though without checking the laptops out personally. Then you can search online (local websites) , classifieds or of course , if you get a good deal , just buy it from a store.