my .02
Best solution (if you can handle it) =
Build it yourself
Second best solution =
I prefer to find a local "whitebox" company that builds PC's and gives a decent warranty. That way you have a local place to go if something goes wrong, they will customize it for you for gaming and most "whitebox" computers can easily be upgraded. In the Boston, MA USA area, I like
www.pcsforeveryone.com. This is probably the best solution IF you have a decent idea of what you want and why, OR if you trust them (find out how long they have been in business. A legitimate business will have references available on request, but might not have a list of "gamer" references)
Third best solution =
See if someone here bought a Dell, Compaq, etc for gaming and is happy with it. Buy that one.
Fourth best solution (first best solution if you have wads of cash) =
www.alienware.com