Check out Alienware, I believe they're now associated with Dell.

Chances are they're overpriced, similar to Falcon-Northwest.
But it is another company that does top end stuff.

I've probably find a local store, if you want a warranty and such.
A chain that has several stores might be decent too.
For example, if I want a warranty and such, I use www.memoryexpress.com
Which is a Calgary based company, but have stores in Calgary, Edmonton, Winnipeg and Vancouver.
They have a program called IPR - Instant Product Replacement; if something goes wrong, you get the same part brand-new, or a better part from the same manufacturer if your part is no longer available.
It is insurance, so chances are the price is more (on average) than it costs the company.
But no questions asked replacement can be nice, if something goes wrong.

Building yourself (which you said you don't want to do), or finding someone who will build it for you... is an option.
If you give them a couple hundred and buy pizza/beer.
Either approach is going to be a lot cheaper then a store/chain.
But there won't be the warranty.