stickness

I am looking of a way to increase stickness to my Drupal powered business index.
Light games seem like an interesting option.

Some ideas:
1. Random picture => identify the business.
2. Weekly Polls with Prizes.
3. Crossword / Puzzle module (e.g. like here).
4. Complete tasks to earn points.

Which modules do you recommend?
And do you have other game ideas which encourage stickness?

Thanks in advance,

Amnon