WinSock Development Information
Sample programs, technical articles, links, and an extensive WinSock error reference. (Bob Quinn)

FreeBSD: Sockets
FreeBSD Developers' Handbook chapter about using sockets

sockaddr.com
Programming Resources for WinSock 1.1 and 2 including sample programs, specifications, and links. (Lewis Napper)

Windows Sockets Programming
Links to get started with WinSock programming. (Ed Snible)

RFC 2292: Advanced Sockets API for IPv6
Defines some the advanced features of the sockets API that are required for applications to take advantage of additional features of IPv6.

Windows Sockets 2
Developer documentation of Winsock for all Windows platforms.

TCP/IP Raw Sockets
MSDN documentation about Raw Socket specification. Raw sockets can be used to create your own protocols.