Here are a couple of proto's you won't find everyday:

Items Listed in Atari 2600:Gamesemo/Prototype

Power Lords Atari 2600 Prototype
http://www.gamegavel.com/item.cgi?show_item=0000487036
Starting At $0.01 Ends: April 3, 2011 9:30:00 PM EDT

Adventures of the Pink Panther Atari 2600 Prototype
http://www.gamegavel.com/item.cgi?show_item=0000487034
Starting At $0.01 Ends: April 3, 2011 10:00:00 PM EDT