MPEG

MPEG Industry Forum
Formerly known as M4IF, it now provides news and resources related to the MPEG-4, MPEG-7 and MPEG-21 standards to help with their adoption and use.
http://www.mpegif.org/

MPEG Pointers and Resources
Annotated links of MPEG resources, focused mostly on the MPEG-1 and MPEG-2 standards.
http://www.mpeg.org/

Xvid
Open-source compression codec based on MPEG-4 ISO format.
http://www.xvid.org/