Any CE plastic is worth big bucks. The most common are the Valk, Firebird, Teebird, Eagle, Leopard, and classic Roc. The CE Roc command big bucks as well. As the runs go up in number, the price goes down. The old Pro Line plastic is good to find as well. The Pro Line Gremlins are a nice find, so is the Cobra. Black discs seem to be coveted, bottom stamp discs too. The old stand by, are first runs. Might go up in price, might not. Good example is the Boss. You can alway play the Champion Roc game, but it can be kind of crazy. Hmmmm, I guess any out of production disc might go up in price, but you never know. Another example. I bought a couple used Z Hawks for $60 bucks, but they are very hard to find. Hope this helps.
To back Rescue, CE discs are a good find. Some Champion Fundraiser discs are good, depending on the make and the year. CFR Destroyers from the first year Innova put Destroyers as a Champion plastic are good for trades, money right now. Certain discs with certain stamps are big. The Radioactive (so I've heard it called) Nuke is big right now too. It's the proto Nuke, all black, and has a small yellow radioactive symbol along the outside rim. Anything before a KC 12x signature disc (11x, 10x, 9x....) is usually good for a bonus if you try to sell. Lots of old stuff, really.
Augusta Wraiths, APX Swirls, and Tulsa Orcs are some other collectible runs. When it comes to 11X plastic, the "pearly" ones are the discs that command the highest price tag. I sold a non-pearl 11x Teebird for $19 shipped online, but if it were a pearly one it could have easily brought twice that much. I'm particularly fond of the pearly 11X Firebirds myself and am always on the lookout for reasonably priced used ones to add to the stock.