Many companies have set up facebook pages to display information and interact with their customers. Since users must be logged in to fb to access the company's page it's easy to collect user data. These apps are often contests.
f'real - Win a Day in f'reality
Contest including video upload to YouTube.
Echo USA - Dislikenator
After liking the app page, users can select which item they dislike more or enter the contest. I wrote the contest form and a simple api for the flash game.
Glenfiddich Cask of Dreams Facebook App
A simple facebook iframe Page Tab that uses FB.Canvas.setAutoResize().
It's my first facebook app!
User's can get a "personalized" message (randomly selecting 1 of 6) added to their wall from the Team Chevy driver or can download an image that adds their profile picture to a collage of Chevy drivers. In the first day there are already a couple of hundred likes.