I feel that I'm a fairly informed member of the AFOL community. I probably see 80% of the LEGO news and information that comes across the interwebs because of my involvement with the site. So I'm often surprised when I find a new trove of existing information that hasn't come across my desk.
Earlier today Flickr member Highonbricksshared a picture that was labeled 'Space Police 3 Proto Drawings' (you can see the image above). Several people asked where the picture was from to which he replied 'research'. Jumping to action I sought guidance from the love child of Sergey Brin and Larry Page (AKA I did a Google search), and I quickly found that Brickpedia has a 'prototypes' page where images of TLG protos can be found. There's a mixed bag of stuff in there, but there's an entire section dedicated to minifigures.
You can easily see from the image above which figs made the cut on Space Police 3 and those that didn't. There's are also early sculpts of the heads from Atlantis and a fig from a line that never launched called 'Seatron' (perhaps supplanted by Atlantis, me thinks).
Lot of great stuff to see! You can find the page on Brickpedia.