Camstasia lets you record videos specifying the source of the sound and even active the webcam if needed.
Once the video is shot, you can edit it with a specific tool with filters and many options.
When you finish your video. You can share it via iTunes, Screencast or YouTube. Alternatively, you can export it as a video file in Flash 3G, AIFF, Quicktime, AU, AVI, Wave, MPEG-4, etc.