A simple passphrase generator, based on a word list of 8829 common English words. Words shorter than 4 characters are not included.
Why use a passphrase? Simply put, a passphrase has higher entropy - in other words, it's harder for a computer to guess - than a moderately long password. At the same time, a passphrase is often easier to memorize than a sufficiently long password would be.
For example, a 8-character random password composed of alphanumerals and four most common special characters (thus 66 different characters - capitalized characters included) has an entropy of log2(66^8) ~= 48. That is, you need 2^48 guesses to go through all possibilities. But such a password - say, b8xL&dl1O - is inconvenient to memorize. Meanwhile, a 4-word passphrase composed from 8829 possible words has an entropy of log2(8829^4) ~= 52! So not only is "letting novels warming harper" easier to memorize, it is in fact harder for a computer to crack than a totally random 8-character password is.