For what purpose? Most of the ones I know of are cross platform applications that happen to have a Mac version, like VLC media player, Handbrake, Audacity, AviDemux, ffmpeg (and gui's for it like WinFF and ffmpegx), and MediaInfo.
Those are primarily video tools. You can see a whole list of video tools for Macs here: http://www.videohelp.com/tools/sections/macos-video-tools Some of them are very high end, and quite expensive, like Final Cut Pro.
If you are looking for other tools, Google is your friend: http://www.google.com/search?hl=en&client=firefox-a&hs=QQn&rls=org.mozilla%3Aen-US%3Aofficial&q=best+applications+for+mac&btnG=Search&aq=f&aqi=&aql=&oq=&gs_rfai=