Secure passwords are hard to come up with and remember. Things like Key Ring for Palm are good, but it means you have to have your Palm Pilot on you constantly. Even worse is something tied to your desktop/laptop. Since the only thing I reliably have on me most all times is my wallet, a paper based solution is best.
I got the idea for this from ./. You have a matrix with the alphabet and random letters, then choose an easy to remember word for each site.
So for GMail my password might be 4pfMnrMIZb. For extra security, in case someone finds the card, I can always prepend with something extra not on the card (maybe always put a ! first or something).
Latex/awk sources to make a business card sized PDF of random letters available here. Laminated it should make a fairly decent increase in online personal security with minimal effort.