Great job on the Mongul entry, Bill! If you're taking requests for pictures to do, what do you think about adding him to the list of possible subjects?
I just put together an entry for Professor Potter and found a great resource - I don't know whether or not this has already been mentioned here, but at
http://www.comics.org , one of the search options is to search by character. Then every story the character has appeared in is returned in the results. I have no idea how accurate it is, though.