I have an Asus g73 series of laptop and it is quite nice. It has a first generation i7, 6gb of ram and 5800 series gpu (cant remember exact one) and I can run just about anything. I got this laptop second hand, the main thing to watch for is cooling. The guy that had it before me did not use a cooling pad and must have had a cat, lots of hair inside the heat sinks. He said he owned it for about 2 years and I have now owned it for about 1 year. The only thing wrong is the touch pad gets a bit weird and stops working. I disabled it and use a wireless mouse with it, the touch pad and buttons are kind of meh in this series anyways. The laptop it self is sturdy and I do everything on this thing from virtual machines to gaming.
A place that I was told to look for laptops was xoticpc.com (
http://www.xoticpc.com/).
For the IBuyPower laptop that looks to be a Clevo and generally that brand is good from what I have heard. I personally have not hear much about Alienware since Dell bought them so I cannot help you there. I would recommend something that can take two hard drives, I have a SSD for my os and most used programs and a rotational disk for game installs and everything else. I do more than just game so I need the extra space. It is really nice to boot windows or linux and browse the internet in under 30 seconds.
I hope this helps.