I have oscillated between different systems at different times
System 1:
use a different email address for each site (i own a domain) and one of a set of 4-5 standard passwords. Easier for me to re-guess what email i would have used (or look at the confirmation email I saved, if push comes to shove).
technically if one site gets compromised and the passwords found, there's no risk that an automated tool be able to get access to other sites but a human going through it by hand just might.
Weakness: sites that want an username, not an email, usually without special characters and often of limited length. Can't be unique and memorable with that.
Scheme 2 - when i cant tweak the username
Passwords usually based on a book title or lyric - in one word or compressed (eg: "The Chronicles of Thomas Covenant, the Unbeliever" could create tcotctu9494) - actually one of my most used ones is based on a book that I never read but meant to read for a while, that i dont even own, but has a memorable title. Particularly good if the site has a question/reminder note field to give yourself a prompt.
Old phone numbers you still remember but which are long dead are also wonderful passwords and can always be re-found in an address book or old card later on.
Scheme 3 - lately i just let lastpass generate and store passwords for me for most sites except key ones which I just need to remember whether i have lastpass available or not
I also have the additional constraint that it needs to avoid keys that change between UK, US and Swiss keyboards - zy especially move around a lot, so does @ and slashes etc. - if your fingers know the password better than your head, it can entrap you when travelling (the french keyboard is a horror, for example - A is elsewhere, and all numbers need shift)
PS: Sites that allow a prompt are great for that, you can give a hint that helps you.
I figured out my fathers passwords thanks to prompts - the prompt was "grosse tete" (big head) so I tried his name and nickname, then, duh! mine. Gee thanks dad! Not very secure even though he usually added parts of my birthdate...
