The system requirements for Guild Wars 2 are likely to be moderately low (my conjecture) and I KNOW the requirements for TOR are low, so really, most lower end systems should run it. However, ideal build would be basing it off the new Intel i7 2600 processor, one of the best you can get and at a reasonable pricepoint. I'd couple it with a Gigabyte motherboard and a 4GB stick of DDR3 1600+ mhz, and as for the GPU, well, the nVidia ones are nice kit, but the AMD/ATI ones are cheaper and about if not more efficient (It kills me to say this). I'd look up a graphics card performance comparison (sites like Atomic PC and Tom's Hardware are a good place to start). You can easily top a 420 for performance at lower cost. Now, depending on your nationality, choose an online computer store, (I'm Australian, so I use umart.com.au and PC Case Gear), and put in your parts and request assembly, +50 bucks for assembly, usually save around 100-120 bucks simply by doing it online, 50 bucks or so for postage, you come out on top with a build you couldn't get in a store. A friend did similar recently and is getting something similar for $1200 AUD, with an ATI 6970 or similar, with an extra discount though. Getting it custom is usually cheaper, I'd spend a fortnight on research, make sure you're up to date, fire off some emails to the assembler before ordering, you could get a great gaming rig, even to run easy to run games.
Sorry About the wall of text.
I'd recommend against the i5's, they're going to be bottom run VERY soon, new i7's, the "Sandy Bridges" are already coming, and some have predicted an i9 model for the near to distant future. As much as I like nVidia's tech and ethos, I would recommend against their cards: They're expensive. Make sure you are getting the best card for your money.
GLORY TO WINDOWS AND BLUE LEDs!!!!!!
Sorry About the wall of text.
I'd recommend against the i5's, they're going to be bottom run VERY soon, new i7's, the "Sandy Bridges" are already coming, and some have predicted an i9 model for the near to distant future. As much as I like nVidia's tech and ethos, I would recommend against their cards: They're expensive. Make sure you are getting the best card for your money.
GLORY TO WINDOWS AND BLUE LEDs!!!!!!