There’s been a number of Mac-app focused contests/promotion sites recently.
Maczot – The oldest, I’ve bought a few apps from this site already.
MyDreamApp – The people’s contest to have your dream app built.
MacHeist – By the dudes behind MyDreamApp, solve a mystery, get some apps.
And the most recently live, MacAppADay. This is the easiest one. Go to the site every day in December and get an app. Done and done.