Links

Doom9.net: The Definitive DVD Backup Resource. A lot of useful guides for encoders, subtitlers, etc. Forum is also super.
Doom9's Forum > MPeG-4 and Co. > New A/V Formats: Upcoming audio and video codecs, new media formats like Ogg, Matroska and MP4.
CoreCodec.com :: The Future of Audio and Video: Matroska, USF subtitles, etc.
The Core Media Player: Newest player in beta status: will support MKV
Media Player Classic: Recommended player, supporting AVI, OGM, MOV, RM, etc.