I'd like to put another vote in the ring for reconsidering your stance on not building your next PC. Barring that, here's my generalized Desktop PC brand estimation:
Good:- Gateway (Your may be interested in their
FX line.)
- Alienware
Decent:- Acer
- Asus (For work, at least.)
To Avoid:- Dell (Inferior Components)
- Compaq (Nothing but bad experiences)
- Hewlett Packard (Price doesn't match the sum of its parts)
No doubt everyone and their dog will find something disagreeable with the above list, but you might be able to generate some kind of consensus after the fallout.
As a parting thought, whatever your brand, you'll probably want a computer with a processor from Intel's i7 line and maybe a graphics card from NVidia's GTX line (275 and up) if you want the computer to fight off obsolescence a little while longer, game-wise.