My favorite contest, was Father Guido Sarducci's 'Find-a the Pope in the Pizza' contest from the original Saturday Night show.
Since that one may not be appropriate, how about a 'Nukeworker Scavenger Hunt' where you send people searching through the site for information, pictures, quotes, trivia, etc. The contestants have to IM you the links to the pages that the information is found on. First one with a complete list wins. Of course, you would have to make some hard to find (i.e. not searchable) but I am sure you could come up with something obscure.
Or, maybe a 'Nukeworker Treasure Hunt'. Give a clue as a starting point which leads to another part of the site where another clue is found leading to another location, etc. Make a labyrinth that leads people through the site... they may even learn something on the way. The last stop on the way would be a password to send to you to prove they got there. You could open the Gold Member section again for the hunt so people could get an idea of what is there. Maybe even the contestants that don't win will be inspired to join after getting into the heart of things.
That is the best I could come up with off the cuff, but I will keep thinking. Well, for a little while anyway... it is Friday.