A great writeup on all that was involved for one person to dream up, develop and market an iOS app - Repeat Timer Pro ($1.99).

Repeat Timer Pro
However, in my search for a solution, I found that many others were also looking for a repeating timer for various applications. I saw this unfulfilled demand as a reason to create my own iPhone app - something I have been wanting to do for a while.

Scratching your own itch is one of the keys to success in the wild west of the App Market. If you can't find an app to do something you want, there's a good chance others can't as well.

Article link via ShawnBlanc.net

Repeat Timer Pro - Repeating Interval Timer - Artem Lapitski

Behind the App: Repeat Timer Pro