This kind of caught me by surprise as I've never seen one before and I am a huge 5200 collector. This may or may not go in the guide but it is a cart case that fits 5200 games, here's the Ebay link.
http://cgi.ebay.com/ws/eBayISAPI.dll...193106732&rd=1
Here's another auction that states a Wico Trackball that is for Atari 5200, I have been emailing the seller for as much details as I can get, I am trying to find out which size plug is has on it and whether it needs the y cable or not, I asked him if it was for the 2600 but he said it was definately for the 5200, as soon as I have concrete proof for a yes or know I will definately post it here. If anyone knows anything about this please chime in, if this is real it's insanely rare as I've never heard of one or seen one before. Even if this is for a diffrent system just mull over this marvelous collection.
[/url]http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=8194476154&rd=1&sspage name=STRK%3AMEWA%3AIT&rd=1[url]
Also the Y splitter says unknown for manufacturer, I have one and it says wico on it, so walala, also these are less common than the Wico Joystick, as I constantly find sticks with no y cable with them, I would list it as a R6. I have seen an average price of $18-$20 each, so put the value at $19 and it should be a safe DB value.