I came across this today:
The mass media may be enamored of the rags-to-riches stories of developers on Apple's App Store, but it isn't the only game in town for indie developers to strike it rich. We've gotten word from SocialMedia, a popular ad platform for social network applications, that one of the company's clients pulled in over $700,000 in advertising revenues from their Facebook apps in December alone. Granted, this was spread over 30+ of the client's applications, but the company only consists of a handful of (very prolific) developers.
I found a good article over at softwaredeveloper.com on how to get started... I'm going to read up on the basics listed below:
1. Anatomy of a Facebook Application: A quick overview of a Facebook application; useful to familiarize yourself with the process before starting out.
2. Facebook Developer's Platform: From documentation to resources and tools, this is your one-stop resource for achieving deeper integration between Facebook and your app.
3. Facebook Developer Documentation: A beginner resource for details of the API, as well as the Facebook query and markup languages.
4. Facebook Step-by-Step: Now that you have the background, Facebook's official application guide will walk you through achieving "Hello World" Facebook integration.
5. Facebook FAQ: Answers the questions that Facebook developers most often ask
Now I just need a good idea...I will keep you posted.