What should it be, to make sure everyone has a chance to enter??

I think a picture contest would be neat. Almost Everyone has pic of the fishy friends. 

How about if we each take a pic of our favorite tank that is currently running (honor system here).  Then
, Jon puts the pics into a thread of pics, no names on the pics, and we all vote on favorite one?  We could have several winners such as biggest tank, most colorful, most fish, most high tech, best planted, etc.  Someone else can come up with prize ideas.
Barb