Craft a formula that you can remember, and then your passwords fall into place. For sites that don't matter, I always use the same simple password. If El Barto suddenly gets banned from here for a flood of gay porn, that'll be the explanation. For sites that I need to keep secure, I usually have 25-35 characters, each unique, alpha/numeric/upper/lower/symbols, and since they follow a simple pattern you don't have to remember them insomuch as you reconstruct them. It also means you can easily change your password from time to time without having to remember all new ones.
Anyhoo, an example system would be some category, like breads of dogs. Pick examples that utilize the initials of the site you're trying to set up. So for PetsOvernight.com, you can use Poodle and Otterhound. Work in a set of numbers that remains constant, like an old girlfriends phone number, and capitalize/shift oddball characters, like the third letter in each word and the prefix. poOdle123$%^7890otTerhound Good luck cracking that one, and if you feel the need to change your passwords, then convert them all to star names, with the same pattern. poLaris123$%^890orIon Since there's an infinite number of categories, you'll never run out of viable options, and since you can use foreign words and proper names, dictionary attacks won't work, either.