if it supports SLI 680, like in your last post, it'll fit any of those cards. Best option supported could be dual R9 295X2's, which will be around $3000, which is probably not what you want to pay.
For SLI/Corssfire 780/Ti/R9290/X, you'll need a pretty big and high quality PSU, preferably 800W minimum, but high quality.