Vanilla Baby is a professional video editor, with which you can create and mix images and sound from any video source (cameras, files in your PC, etc).
During the process you can preview both the two channels that make up the mix and the resulting video. You also have a multitude of video transition effects, you can include any MP3 or WMA file you have on your PC as the sound, and insert logos (or watermarks) in the final video. The resulting video format will be .wmv, but it is easy to convert to any other format you want.