Diamond Viper V330 4MB then added a Diamond Monster 3D for that extra "Oomph!" which really didn't pan out very well. Then moved up to a Hercules 3D something or other, a Radeon 7000, Radeon AIW 8500, Radeon 9800 Pro, X800, X1900GT, 8800GTS 320, 8800GTS 512 and finally the GTX 260s in my sig.
Haven't upgraded in a while, just haven't got the time for gaming like I used to. Only reason I would even consider upgrading these days is for significantly higher F@H PPD.