Evga has extended their trade in program from 90 to 120 days in celebration of the 9800 GX2 launch. Be advised that this is a limited time offer and that after the offer is over, the program will go back to 90 days.
BFG is launching their "Trade Up Program" today. Their program features a 100 day trade up period but only graphics cards launched after February 21 2008 are eligible right now. That means that if you bought a 9600 GT, you can trade up to a 9800 GX2. That is a "trade up" of over $400. Their program will probably become more attractive after cheaper 9,000 series cards (like the 9800 GTX) are launched.