The strongest passwords are ones that don't contain actual words. Firefox extension ObPwd generates strong text passwords from images or text on your computer, so you can re-generate them when you need them but don't need to resort to weak, easy-to-remember passphrases.
While we love online password managers like LastPass, many of you don't feel comfortable storing your passwords on someone else's server. If you want strong passwords without a manager like LastPass automatically entering them for you, ObPwd is an interesting alternative.
With it, you can right-click on any text or image from a webpage or on your local machine to generate a strong password for you. That image or text will always generate the same password, but it won't be something someone can easily crack if they have one of your passwords (or know you well). You can then use the same type of object on all your frequented websites — like the site's logo, or the first sentence of the second paragraph on a page — to generate all your passwords. It's a pretty interesting way to generate passwords, and one few people are likely to think of if they're trying to crack yours.
That said, the one downside is that if you use images, text or files that end up changing, you'll be SOL. I'd recommend still storing your passwords in an encrypted file somewhere on your hard drive, or somewhere safe and local the first time you generate them. That way, if a site updates and you lose your password-generating image, you'll still be able to log in, then change your password to a new one.
ObPwd is a free download, works wherever Firefox does.