IMTC Packet Switched Streaming Activity Group
Group of network infrastructure manufacturers, carriers, handset vendors, streaming multimedia vendors and content providers working on interoperability surrounding streaming media protocols.

Internet Streaming Media Alliance (ISMA)
Group promoting the use of RTSP, RTP, and a subset of the MPEG-4 specification.

RFC 2326
Official RTSP specification, published by the Internet Engineering Task Force (IETF)

RTSP: Real-Time Streaming Protocol
General information about RTSP provided by Dr. Henning Schulzrinne of Columbia University

SourceForge RTSP Specification Tracker
Official issue/errata list for RTSP, from which the future version of the RTSP specification will be made.

Unofficial IETF MMUSIC WG Page
Information about meetings and documents of the Multiparty Multimedia Session Control WG within the Transport Area of the IETF