There is a collection of free mac video converters to help mac users to handle nearly any file format.
MPEG Streamclip is a powerful free video converter, player, editor for Mac and Windows. It can play many movie files, not only MPEGs; it can convert MPEG files between muxed/demuxed formats for authoring; it can encode movies to many formats, including iPod; it can cut, trim and join movies. MPEG Streamclip can also download videos from YouTube and Google by entering the page URL.
FLV2iTunes is a simple docklet application for converting movies to iTunes,iPod, and iPhone supported format.You just need to drag and drop movies to it and you just need to wait. It will accept any movies format that are supported by ffmpeg (WMV, XVID, DIVX, FLV, AVI, and more), converts it, and insert the movie into iTunes library.
HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded video transcoder, available for MacOS X, Linux and Windows.
When you finish your iMovie project, you have multiple ways to finalize it: save onto your computer, transfer to iTunes, share to YouTube, Facebook and more if you’re using iMovie 09 and iMovie 11. However, you may still consider exporting iMovie to DVD to better preserve it or share it.
Media Converter is similar to ZamZar and vixy.net, but requires you to create an account and log in. Also, it seems like it only supports downloading and converting videos from YouTube. You can also download their video download program, but it only supports 5 sites.
VideoDownloader is a FireFox extension, but also allows you to paste in any URL from many sites such as Blip.TV, iFilm, and even social networking sites like MySpace. You can also download a free FLV player from their site to play the videos.
Movavi Online is a free online web service that lets you download videos from YouTube, Google and other video-sharing sites and save them to your iPhone, iPod, cellphone, and popular video formats: AVI, MPEG, MOV, FLV, MP4, 3GP.