I use a mental algorithm that generates a unique password for each site. It's easy to remember the algorithm and I get a complex unique password for every site. I don't think a password existing outside of your head makes sense.
(though some sites force unique passwords/and password changes, which can be annoying as I have to remember to bump a value mentally for how many times i've been forced to do it, luckily for the most part it's not an issue)