Here is a list of High End Gaming Machine Alternatives that are Alienware Alternatives with some of my personal positive experiences and some brief notes on each:

GAMING MACHINE - Falcon Northwest - If you are looking for a very high end machine this is the company you want to check out. Prices are high but with my personal experience with Alienware it actually ended up costing me way more than I would have spent with Falcon Northwest. My personal experience with Falcon was years ago (can't remember the system specs) but it was a very positive experience and the machine lasted for years with minimal headache. ResellerRatings.com to Falcon NW - if you buy from them be sure to post your experience (good or bad) to help others make a better decision.

GAMING MACHINE - Gateway - this was the latest gaming machine before Alienware. It is about 3 years old and I never had a problem with it. I can not remember a time when I needed to call tech support. The computer still plays the gaming that I am interested in (i.e. Battlefield 2) and is more stable that the newer Alienware.

GAMING MACHINE - Dell - prior to the Gateway I owned two Dells in a row. I did have to call tech a bit with each, early on, but the issues did settle down. Hold times on the phone were long, tech support did correct my issues quickly without making me jump through numerous hoops.

GAMING MACHINE - iBuyPower - I was looking at this company and Alienware. Their prices are cheaper but I was nervous about never hearing anything about them. Plus it seemed they were very focused on creating zany cases, that makes me nervous. I want the focus on the guts of the machine not the case that is going to sit under my desk. I have no experience with them.

General Use COMPUTER (not good for high end gaming) - Emachines - I purchased an emachine for my daughters. They beat it up pretty good and it keeps on working. I have not had to do any tech support calls since buying it. During my research I got a hold of tech to ask about the computer listed on their site being different from the one I bought at BestBuy. The support guy was very helpful even when I had the wrong department and he had nothing to gain from helping me... other than doing a good job for the company itself. (it wasn't his job but he helped - and that is why I bought the machine.)

LAPTOP HP/Compaq NC6000 - This is my second HP in 4 years. First one the motherboard fried. This one is still going strong and I put a lot of miles on it. It travels all over with me from BTV to RSW to OAK to LGB (to name a few. It is good for work and very limited games. Forget playing high end games on it.

I know nothing about these companies but it might be worth a look
Voodoo PC
ABS
Hypersonic

Be sure to check the company rating on ResellerRatings.com - Here is a link
ResellerRatings.com for Alienware