Medical applications for the iPhone.
I recently received an email from a doctor in India who wanted some advice about a medical iPhone app he created. I encouraged him to post the idea on the linkedin site for the Society of Physician Entrepreneurs and harvest the "wisdom of the masses". Shortly thereafter, he posted a beta version of the app, a clinical simulation tool similar to case of the week, and asked users to provide feedback. A few weeks later, another email relayed that "My iPhone application has been a smashing success - I've had close upon 7000 downloads so far and it is the 7th most popular medical application in the United States". In addition, he was chosen to present his startup idea to the Mumbai Seedcamp at http://seedcamp.com/pages/mumbai10
Here's a useful article about how to get your iPhone app approved and how to make money from the idea. This is yet another example of the Long Tail theory and how you can benefit.