A friend recommended to me substituting easy-to-remember numbers and other characters for certain letters: for me, ( = C/c; + = T/t; 4 = A/a; 9 = G/g; etc. I coupled that with one rule: I capitalize every other actual letter used. That way, a strong but easy-to-remember password tailored to each site (its name, function, etc.) is easy to do--adding (in my case) a favorite expletive if it needs to be extended, or just because I hate the sponsor of the site (bank, insurance company, etc.).