I had some pictures of prototypes that I had in my archives, and I finally got around to posting them. Thanks to Retrology (a member here), who sent most of these to me. Cybernator Mega Man X3 Stunt Race FX Syndicate Theme Park I always welcome more contributions, especially dumped prototypes.
I had a proto of Cybernator at one point in time. It's 100% the same as the final release apart from it has a sound test and features the anime characters on the option screen. The game was still censored like the final release and still missing part of the ending. I prefer the original game by NCS Masaya for the SFC.
There is another Mega Man X3 prototype that uses a different kind of board (saw it on d4s' website). I don't know who has that one, though, nor if it is also final. I'm pretty sure if you wanted to see something significantly different, you would have to find a Rockman X3 prototype. I did release a Rockman 7 prototype a couple of years ago that did have significant differences, so it is possible that it could be out there.
Here is a Super Mario Kart prototype. Identical to final, unfortunately. http://www.snescentral.com/review.php?id=0166&num=0&fancy=yes&article=proto
It's too bad that that proto isn't different from the final. Also, are you the owner of Snes Central, badinsults?
There was a second Super Mario Kart prototype that was sold around the same time that apparently had different music. I was never able to get a response from the guy who bought it though.
The person who owns the other prototype sent me a bunch of pictures. Check the Super Mario Kart page on my site.