Word-based passphrases that are easy to remember but hard to crack
A 4-word passphrase has roughly the same entropy as a 10-character random password. However, passphrases with 5-6 words are both more secure AND easier to remember, making them a practical choice for master passwords.
The XKCD method (from comic #936) suggests using 4+ random common words as a password. 'correct horse battery staple' is easier to remember than 'Tr0ub4dor&3' and is actually more secure because of the combined entropy of random word selection.
4 words is the minimum for decent security (~53 bits of entropy with a 7,776-word list). For high-security accounts, use 5-6 words. Each additional word roughly doubles the crack time.