OpenSSH:An open source SSH client and server.
IETF Secure Shell (secsh) Working Group: Contact information and papers of a group standardizing the SSH protocol.
OpenSSH on Windows: Port of OpenSSH server and client for Windows.
SSH Communications Security: Extensive information about the SSH protocol. Has a variety of SSH products for sale, including clients, servers, and VPN software.
SSH Master FTP Site: Binaries for SSH1 and SSH2 clients and servers for Windows and Unix.
SSH Patch Repository: NCSA's collection of patches for SSH.