Originally Posted by
Ghâzh
The nvidia 750ti would be the best option. Costs about $150, doesn't need additional power cables and can be ran with basically any PSU. Plus it's really small so it should fit in any case.
Please do note however that this upgrade might not improve your FPS in those games noticeably. 750ti is considerably better then your old gts 450 but you are most likely limited by the rest of your older system in mmos. Although it's a nice card to keep should you wish to upgrade the rest of your system later down the road.