Sockets

FreeBSD: Sockets
FreeBSD Developers' Handbook chapter about using sockets
http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/sockets.html

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.
http://tools.ietf.org/html/rfc2292

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

TCP/IP Raw Sockets
MSDN documentation about Raw Socket specification. Raw sockets can be used to create your own protocols.
http://msdn2.microsoft.com/en-us/library/ms740548.aspx

Windows Sockets 2
Developer documentation of Winsock for all Windows platforms.
http://msdn2.microsoft.com/en-us/library/ms740673.aspx

Windows Sockets Programming
Links to get started with WinSock programming. (Ed Snible)
http://www.snible.org/winsock/

WinSock Development Information
Sample programs, technical articles, links, and a WinSock error reference. (Bob Quinn)
http://www.sockets.com/