This will evaluate passwords for strength. The results are surpising, some passwords I though were "best" only came back "strong" and vice versa

https://www.microsoft.com/en-gb/security/pc-security/password-checker.aspx

Wikipedia has a pretty good article on password strength
http://en.wikipedia.org/wiki/Password_strength#Entropy_as_a_measure_of_password_strength

And just for chuckles, the 25 most common, and worst passwords used in the last year.
http://www.slate.com/blogs/future_tense/..._about_you.html