Audacity is a free recording software that is compatible with both PC and Mac. What Audacity lacks in thrills, such as high quality effects and mixing capabilities, it makes up for in simplicity. The interface is very straightforward and takes a minimal amount of time to learn.
GarageBand is a recording software that comes already equipped on MacBook computers. GarageBand offers a bit more options than Audacity, such as effects and more detailed sound mixing options, but it also only works for Macintosh computers.
For those who are Mac owners and have a bit more experience with recording and editing audio, Logic is the most "logical" step up from GarageBand. As of August 2010, Logic Express 9 costs $199 and Logic Studio costs $499. It is easy to move projects from GarageBand to Logic if you decide the make the upgrade late on.
ScreenWatch is software designed specifically for recording lectures in the classroom, but it could also work well for recording a sermon. The software enables the user to not just record the audio but also features video recording capabilities if you have a camera and the potential to do a live video stream. Plug-ins for web streaming come with the program.