Bitdouble doesn't have a contest but in a way it's similar to wagering contests since they give rewards to their weekly and monthly top gamblers. There are three paid places for monthly and weekly the prizepool is 120mbtc(monthly) and 12mbtc(weekly).
Added and I checked the prize distribution, there are 30 paid places for each contest.
My bad, I forgot to scroll down when checking their leaderboards i'm always used to seeing the top 3 since they post it on their thread. With 30 paid places the correct prizepool is 210mbtc and 21mbtc.
Bitkong also have a weekly reward for their top gamblers but the prize pool isn't fixed it seems like they're based on the site's profit. I tried looking for a clear definition but their bonus page didn't explain much the closest i've found is this post.
Our Leaderboard bonus is some kind of wager contest, where bonus pool generated by total wagered amount. We send this bonus daily, weekly and monthly.