If you are using a mac or PC and want to add Vorbis (*.ogg) and FLAC (*.flac) playback to iTunes and Quicktime then these two apps are very handy. I just recently installed them and they work great. Fluke is used to add FLAC playback and XiphQT is used to add Vorbis playback. Instructions to install and use these apps are included on the Fluke and XiphQT websites.
FLAC and Vorbis are both open source compression formats. The popular mp3 and AAC (Apple) formats both have proprietary technologies in them. FLAC is popular with the classical music sect because it is a lossless format. 100% of the audio is preserved but less space is needed tp store it. Some popular artists like Brian Eno and Perl Jam have began to embrace FLAC as well. Vorbis is a lossy compression, like mp3, but it does not use propriatary technologies and some say it sounds better than mp3. For more info on these formats check out these links: FLAC, Vorbis.