...The passphrase-generator defaults to only 3 words instead of the 4 suggested by XKCD, but uses a larger dictionary found in many unix like systems at /usr/share/dict/words. It also provides estimates for the entropy of the generated passphrases. The randomization is based on /dev/urandom and SHA1.
See http://xkcd.com/936/ for an entertaining take on passwords vs. passphrases.
See my post in stackoverflow for links to other solutions and discussions on passphrases vs passwords: http://stackoverflow.com/a/12646320/1148030