The problem here is that the problem is exactly the same as any startup -- ideas don't mean a lot. By that I mean that most any idea I could come up has probably been tried before. The trick will be finding a developer who is deeply immersed in the culture of folks they're tying to help and can speak to them.

Anonymously identifying officials that asked you for a bribe. That'd be a great app.

Finding the nearest potable water.

Job search for unskilled workers.

Craigslist for illiterate people (add in geo-location instead of cities)

Most especially in this market -- remember to develop for eyeballs, not money. That is, if you get enough eyeballs? You will be extremely rich.