I have an older Alienware. The computer works great!! A real beast.
However, I had one problem with the mainboard and the customer service from Alienware (before DELL purchased the company) was atrocious!
So, in my experience, I would say Alienware makes good computers, but has lousy customer service. Hopefully, Alienware has improved their repair servicing since being bought by DELL computers.
I've heard good things about the following two companies (I'm looking at buying a new computer in 2010 or 2011):
sorry...new here and cant figure out this inserting link business!! 
check out iBuypower PC and cyberpower PC and Digital Storm PC
OT...how the heck do i post a link????? The insert link button is always greyed out and unavailable. When copy a link and try to paste in the thread I get a message saying that this forum does not support cut and paste.
thanks!