The Apple iPhone is now becoming a medical device as developers find new and innovative uses for it. Medical professional's already have a variety of apps to help them in their jobs. However, new apps are now being created for a variety of people with medical needs.

These apps range from simple tracking applications like the Crohn's Toolkit which helps patients manage their disease better and give better data to their doctors to the soundAMP app that turns your iPhone into a digital hearing aid with record and playback capability.

Here is a list of apps I've found so far.

1. soundAMP - Turns iPhone or iPod Touch into an interactive hearing device
2. Crohn's Toolkit - Helps Crohn's and Colitis patients manage their condition better and
   communicate with their doctors.
3. iPrompt - One of a number of communication apps for use with children with developmental and language delays
4. Behavioral Tracker Pro - Supports tracking behavior and graphing it, including ABC therapy
5. Step Stones - Visual activity schedule for those with special needs or learning disabilities

UPDATE: I have created a wiki info page that anyone can update.