4870x2 or 2 GTX 260s / 2 GTX 280s

2 X2s is basically the top of the market right now, besides 2 295s in some games. I'd go for the 2nd X2 just to try Quad Xfire.

Another 4870x2

i7. Another 4870x2 would also be nice, but kind of overkill on a 24".

I personally wouldn't upgrade your gfx card. Either get another 150gb raptor and run em in Raid 0, or get another 24" LCD or upgrade your cpu and mobo to i7. 1 4870x2 is enough, a 2nd is a waste of money in my opinion.

Biggest performance boost will be RAID 0 those Raptors. The speed increase even in this older Raptor X set, is so much, I'll never have another computer without RAID 0.

OP, if you have a lot of big files (especially video) RAID 0 Raptors will make it much more bearable to move and edit them.

If you are going to switch cards then go for the 280/285 SLI setup. 260's in SLI isn't going to be much different than your 4870X2. I'd hold off on doing any of that though since the 4870X2 is already a beast of a card and apply your money elsewhere.

i think i would have to say sli 285's, then get a third later on, the outperform 2 295's. otherwise i would have to go with raid0 like other people have said, or maybe ssds?