If you're really dead set against building your own then I would say Alienware.

I know the build quality of Dell machines far too well for my own good - They are built by one blind quadroplegics, with no consideration for airflow. The best system they've put together is the top end, water cooled, XPS monster. It's still crapply built, too.

Alienware, at least, have a 'gaming heritage', and their desktop build quality is leagues above Dell - Even though the two companies are joined at the hip. I would suggest Alienware of those two.

If you could, though, find someone who'd build the PC for you (Say, a friend or relative) then you would get infinately more choice of parts, and probably lose a LOT of the cost. Example: What I built for ɤswordhorder cost in the region of £700 less than an equivilently spec'd machine from an 'enthusiast' PC retailer, who're pretty big in the UK, as far as hand built machines go. The saving is obviously dependant on how well you shop for parts, but hey, if you're not interested in that, then s'no big deal.

At least with an Alienware you get a warranty that's easy to deal with :B