So you've got a 780i, a GTX295, and an E8400?
That should run just about anything out there on the highest settings ATM... Only thing I'd upgrade there is the proc, which most will say isn't even necessary, but you can get a 9550 or 9650 if anything you do needs more than 2 cores.
One thing a lot of gamers get screwed by is keeping their old HDD's when upgrading rigs. Running faster hard drives (especially using RAID) can sometimes increase perceived performance more than these bump-ups in the top of the hardware chain. I have 2 rigs, one of which only has an E8400 (3.6GHz), 4GB of DDR3 RAM (1.6GHz), and a single 4870 1GB on an X48 mobo.... And, at the highest settings, blazes through the only 2 games I play (BF:BC2 and AoC).
I haven't played much besides those two games (played WoW up until a few months ago and it ate that up on max settings too), but we're at a point right now where hardware development is rapidly outpacing the needs of the games being developed. Like I said, the only thing I'd recommend is that you upgrade your proc, and that's only if you need the extra cores, and if you're playing at 1920x1200 or below, the vid card is more than adequate....