Corsair Vengeance Blu 8 GB (2X4 GB) PC3-12800 1600mHz DDR3 240-Pin SDRAM Dual Channel Memory Kit CMZ8GX3M2A1600C9B
AMD Phenom II X6 1090T Processor, Black Edition (HDT90ZFBGRBOX)
Gigabyte Socket AM3/AMD 890FX/SATA3&USB3.0/A&2GbE/ATX Motherboard GA-890FXA-UD5
MSI Radeon HD 6950 2 GB GDDR5 2DVI/HDMI/2xMini DisplayPort PCI-Express Video Card R6950 TWIN FROZR III PE OC
Total Cost ~ 800 USD
Thats what Im running, and I dont have issues.
Its important to note that while MMO's do have a dependency on GPU's they also heavily depend on your CPU as well.
Of course you could take the Intel/Nvidia equivalent of the parts mentioned, it would be a bit costlier but not much. I was a long time fan of Intel/Nvidia, until recently I was in your situation, and I just wanted a good value upgrade to get playing again (Rift Era) and I decided to try AMD. I was happy with it and I doubt anyone would be unhappy with it, given the performance for value.
I run all settings at high or highest no issues.