I got this idea from a contest a local radio station had a few years ago.
We (a mod) start a wallet into which anyone (who wants to promote bitcoin) can contribute a however many BTC they can.
This huge pool of BitCoins will be the prize and incentive for people to participate.
In order to win, you have to spread the word about BitCoin int the most spectacular way you possibly know how.
Streak with bodypaint, write a viral song, give out free pancakes with the BTC logo, whatever stunning and creative way you can think of, then post a video or any other form of proof you think will suffice. Bonus points if local media picks it up
The ever growing pot of BTCs will encourage people to pull off ever grander schemes, and community then votes on the most impressive entry.
This would be a great and cost effective way to get BitCoin into the spotlight and get the whole community involved
PS: I got dibs on flying a giant UFO shaped BitCoin blimp
EDIT: There are no "dibs" on anything here, if you copy someone's idea, but you get more exposure, then that's just that much better for bitcoin. The community decides the winner anyway.