Microsoft has a handy utility that rates your passwords. It doesn’t just look at the length of the password, it looks at how you mix upper case with lower case letters, numbers, punctuation marks etc.
When creating new passwords for your online services aim for Good or Best.
Try it here: http://www.microsoft.com/protect/yourself/password/checker.mspx
Note: there might be better password checkers in existence, I suggest this one because it’s hosted on Microsoft’s site. Whether you love them or hate them I believe their intentions are good and they won’t try to steal passwords.
Keepass also has a password security checker, not to mention secure password generation and all that jazz 🙂
http://keepass.info/
Thanks for the tip, Keepass looks like an excellent program. It’s open source so anyone can verify there aren’t any backdoors or spyware included, and it does everything you need to create and store passwords.