Guild Wars 2!

[Shadow]

https://www.guildwars2.com/en/news/b...d-performance/

https://docs.google.com/spreadsheet/...=0&output=html

Note in the last link, the GeForce GT 520 is listed at Low performance at 1366x768.
That's what I had during the first two betas, and I ran at the lowest possible settings. I built a new system because the game was almost unplayable in any sort of group event on my Dinosaur, so I'd go with something listed at Medium at the absolute minimum.
As to your question regarding best bang for your buck, somewhere around these [HD 4770, GT 545 (DDR3) HD 4830, HD 5670, HD 6670] is probably going to be the most cost effective. But going with a lesser rig will mean that you'll have to upgrade sooner, so if you're building a new rig then I'd suggest spending a couple hundred more and future proofing a bit.

I built a rig which can run at max settings with multiple programs running in the background, while recording, and never drop below 40 fps [usually above 60] for around $800.
{MSI z77a-g45 MoBo, i5 2500k CPU, GTX 560 GPU, 12gb RAM, mid tower case, 1tb HD, optical drive, etc etc etc}

If you really shop around, you can build a system that will run it decently for half of that. As long as you're getting 15-20 fps in large group events [which will mean around 30+ in low pop areas] the game is playable. Some people boast about their Hero Rig getting 90+ fps, but the refresh rate of most low end monitors is 60 so anything above that is usually wasted unless you spend a lot on your monitor as well.... which almost no one does.
But again, going with a lower end build will mean upgrades need to happen earlier.
I suggest building the absolute best system that you can afford to build, with the addendum that anything above $1k total is usually wasted. You can get a LOT of computer for $600-$700 if you know what to look for.
Compare that with purchasing a "gaming rig" pre-built for $2500 and you'll see why gamers build rather than buy.