Diceware is a free & open system for creating pass phrases with proveable security quickly and easily, by rolling dice. Diceware pass phrases are easy to remember, and except for broken services where password lengths are limited to just a few keystrokes, the system provides a complete solution. Two words from diceware are more than adequate for most LAN user logins, three for most admin logins, use more for cryptographic security where applicable.

http://diceware.com