RFC Editor: Collates Request For Comments documents. Explains the RFC process, and includes a searchable database of RFCs.
The Internet Report (IETF Weekly Updates): A table of new Internet Drafts and RFC's that come out each week, with synopses. Archived summaries go back to June 1999.
Active IETF Working Groups: A directory of the Internet Engineering Task Force groups and their web pages.
Free Protocols Foundation: Independent public forum supporting patent-free protocols. Includes policies, papers, a mission statement, and a list of free protocols.
IETF Internet Drafts: List of documents organized by alphabetized subjects.
Internet Encyclopedia: Overview of Internet protocols.
Internet protocols: General comments on protocol design, and good reference material on a few protocols (especially mail-related; also ftp, time, and misc) by Dan Bernstein.
Port Numbers and Services Database: Well known port numbers for TCP and UDP, from Internet Assigned Numbers Authority (IANA).
Protocols.com: Features an overview of various networking and mobile communications protocols, white papers, and links of interest.
RFC Sourcebook: Description of protocols, file formats, glossary of terms, RFCs.
The Kermit Project: A protocol that transfers text and binary files without errors between diverse types of computers over potentially hostile communication links, and a suite of communications software programs; Columbia University.
XNS.org: Independent organization managing the eXtensible Name Service, an open protocol and open-source platform for universal addressing, automated data exchange, and privacy control. Includes an overview, charter, history, and specifications.