just a heads up, a brand new 8800gts 512 can be had for $110 at newegg.
for selling the used ones, i dont think you can get a gtx 280 "strait up". you will have to fork out a little more cash.
but with that said, 2x recertified gtx 260's will cost about the same or a little more as a gtx 280, and that would be a really nice jump in performance for you over the 8800's
thanks, i was actually looking at EVGA's Bstock they have a GTX280 for 249.
and no i dont really game anymore, im now using my PC for digital imaging like multiple instances of photoshop.
Sounds pretty pointless if you don't game though....