The number one thing I want most from any iPhone app that plays audio (or video). In particular: Apple’s iPod app, Apple’s YouTube app, Matthew Gallagher’s Stream To Me, and Bottle Rocket’s NPR News app.
The biggest button on the app should be the pause button. The pause button should be separated from other buttons by as much space as possible. I should never go to hit pause and instead find only a spinner. I need to be able to pause even during the time between hitting play and when playback actually begins. (Or, as in the NPR News app, between entries in my playlist.)