So... good return on investment (at least 4 times, otherwise it's really not worth your time - unless of course, you're one of those Ebay scavengers scrapping pennies).
What else?
if 4x is your qualifier then a number of the early releases would qualify, many helped by their low original sale price, but they just don't come up for air that often.
Some others not already on the list:Jay Ryan's Close Encounters is selling for nearly 7x its $20 price. His Ferris is over 10x.
Jaws
North By Northwest RR 07 Kleinsmith
The Good, The Bad, and The Ugly Set RR 08 Perkins is pretty close to 4x even with his art print cutting into demand.
Also, I know that Kleinsmith sold his last GB&U, a truly under-appreciated print, for $200, well above the 4x.
Getting Close:King Kong 08 Burlesque is getting real close to 4x, as it should.
2001: A Space Odyssey 08 Ryan 3x and climbing...