I will assume you live in the United States and can buy from Newegg.
Under $1000
Open Box: CyberpowerPC Gamer Ultra 9214
CyberpowerPC Gamer Ultra 7512
iBUYPOWER Gamer Extreme 931E
The first model - "CyberpowerPC Gamer Ultra 9214" - would perform best in games as it has the fastest video card, however it is an open box product.
Under $2000
iBUYPOWER Gamer Supreme 962i
Great CPU: Core i7 920 (just released)
Great amount and speed of memory too: 6GB DDR3 1333 (can't comment on quality though)
Great video card: nvidia GTX260.
Great chipset: X58 (although I'm not sure on the board itself)
It looked like the best under $2000 PC on newegg: the others had weaker graphics/video cards and/or Core 2 Quads. Core 2 Quad aint slow, but Core i7 is newer and quicker.
All of those PCs would play Guild Wars on max settings. All the PCs with a GTX260 would play Guild Wars 2 on max settings. The 9800GT PCs would play Guild Wars easily, but maybe not everything max.