I've just completed deploying SSH servers to all of our UNIX boxen. It provides strong authentication and secure communications over insecure channels.
All communications are automatically and transparently encrypted.
Encryption is also used to protect against spoofed packets and hijacked connections. X11 connection forwarding provides secure X11 sessions. An authentication agent, running in the user's local workstation or laptop, can be used to hold the user's RSA authentication keys. Multiple convenience features fix annoying problems with rlogin and rsh. Ssh is intended as a complete replacement for rlogin, rsh, rcp, and rdist.