I saw a really good deal so I picked up a Powercolor 7870 XT, which gave me many minor issues as well as artifacting and flickering, which got progressively worse. I swapped it for an MSI 660 Twinfrozr which was fine at first, but over time also developed flickering and rendering errors.
For example, for the GTX 660, in League of Legends, Syndra's balls would be rendered as black squares, and my minimap champion icons could turn black.
Then I swapped it for a XFX 7970. Had problems from the start. When installing the 13.4 driver, I uninstalled the old nvidia, used a driver sweeper for all my old drivers, followed some forum posts to try to find all the registry and various traces left in my computer - it kept giving me a package install error. However, the driver seems to work fine otherwise.
A 13.1 older catalyst driver installs without error. However, opening GPU-Z gives me errors about detecting OpenCL, and I have worse artifacting than 13.4.
Some examples of artifacting:
In League of Legends, I would get flicker artifacts, as if an explorer window alt tabbed in for a split second. This would happen about every 5 minutes, worse while spectating.
In Civ 5, my entire screen at rare times can flicker horribly to make it completely unplayable. Sometimes everything works fine, but when other players contact you for diplomacy, you will see Gandhi's character rendered in blacks and purples and indigo, as if he was a photo negative or something.
What could be the problem? I tried replacing the DVI-DVI cable to an HDMI (from 7970) to DVI, still the same. Another odd issue is that the one of the DVI slots for the 7970 doesn't work if you try to power on the computer with the DVI inserted into that slot, but works fine if you switch to it after its already on. There is some info about the 2 DVI ports on the 7970, one of them is an only digital signal apparently, and another supports VGA adapters.
Samsung SyncMaster2443 monitor
Asrock Extreme3 Gen3
Corsair HX750 (I think this is a possible candidate, my old HX620 fried my previous mobo)
2500k @ 4.7
8 GB Mushkin Silverline
Samsung 840 Pro
Seagate 12? 1TB
Win 7 x64