Podcasting is new delivery method of mp3 files that is recently getting a lot of press. Through an RSS feed an mp3 file can be captured by podcasting software and listened to on any mp3 player or your computer. There is great potential for this to be used for ministry purposes.
You could make available any type of audio program you may produce such as a church service, radio show or presentation.
Andrew Careaga, has more information on hi blog at e-vangelism.com about churches podcasting.