I agree with the Bugking. A terrain contest would be fun but hard to do as large terrains take a very long time and many people paint miniatures but don't make terrains
If you want a kind of terrain contest it could be a little diorama with a few miniatures, like deadly duel entries may be.
I really like the Femme Fatale, Rotten Harvest and Total Testotesrone contests but you could change them with a specific theme, like you do for Iron painter. People could enter any miniature as long as it fits the theme.
You could also have a specific Wyrd contest with Wyrd miniatures only.
I like gift certificates but a trophy for the winners with a bust or a special edition miniatures would be fantastic( like the Forum of Doom contest).