Free jQuery Password Strength Plugin
Websites have a responsibility to users to accurately tell them how good a password is, and this is not an easy job.
If your password is 8 characters long and only formed of lower case characters, you need to make it better, perhaps by adding a number or more characters.
If your password is 25 characters long but happens to not contain a number, you shouldn’t be forced by a password security policy to add one, you clearly have a very secure password.
Complexify aims to provide a good measure of password complexity for websites to use both for giving hints to users in the form of strength bars, and for casually enforcing a minimum complexity for security reasons.