Mac Only. Uses the MediaInfo code base. Adds some UI enhancements. Available in the Mac App Store
Mac only. Also based on the MediaInfo code base. It adds the ability to examine more than one file at a time and has a useful "compare" mode. Available in the Mac App Store
Mac and PC. Transcode practically any source to H.264 (and mp4, mp3, and mp2). Fast and accurate. Offers control of a zillion parameters
Mac and PC. A free video converter with some unique abilities. Unlike some others it handles QuickTime's internal architecture flawlessly.
FFMPEG is the the most influential collection of code libraries in video today. It is open source and is used in the foundations of many of the best video converters available. It can be used from the command line or from a number of packages that provide a GUI for it.
Mac only. An excellent GUI for FFMPEG. Easy UI and a lot of hints on settings.