I just purchased my 3rd Dell Computer ( last week ) from their refurbished "Outlet" website.
Dell allows you to return any computer within 21-days . . . Those that get returned are put back into inventory on the "outlet" website as "refurbished".
The neat thing is that you can easily save yourself $300-$400 from what would have cost to purchase a new machine, AND you get the same 1-year warranty as the new Dell machines.
For example, I just bought a Dell Vostro 400 off of their Business "outlet" site ( they also have a Home "outlet" site ).
The Vostro 400 is a barbones business computer without all of the software crap loaded on it. It has an Intel Core-2 Duo 2.66 Ghz microprocessor with 4MB of L2 cache and a 1333 front side bus. Also got 2 Gigs of the PC-6400 800Mghz memory, with an entry level Nvidia GeForce 8300 GS video card and not one, but 2 hard drives ( 250GB and 80GB ).
All of this is on the Windows XP platform ( too many "bugs" in Vista for my taste ) for $499.00!!!
The only thing that I am upgrading myself is the 300 watt power supply. Dell power supplies are notoriously strong, with superb 12v and 3.3v rails, but I have always gone to PC Power & Cooling to upgrade the PSU. The PSU is by no means a glamorous part of the computer, but it is vital when it comes to supporting extra memory, video card demands, hard drives, etc.
You can get the "Silencer 470" which is a standard ATX design made for the Dell for only $99.00
Throw in a GeForce 6200 video card by BFG Technologies ( 256mb and dual output ) in the PCI-slot in the bottom of the case ( supports 2 more monitors ) for $70.00 and I'll be good to go!
The only other Dell computer that I was looking at was the XPS-420. Unfortunately, they usually come only with Windows Vista and an ATI Radeon video-card.