A great post from the 1Password team regarding your "master password"--i.e., your "one" password--that controls access to all of your other passwords. It's good advice that's applicable to passwords in general.
While on the topic, if you're not using 1Password (or similar)--and you can afford it--then you're an idiot. I'm sorry to be so blunt, but there just isn't any excuse. (Same goes for not backing up your data. It's effectively free these days.)
If you're on the fence because of the price ($40), be sure to check out the Freelance Mac App Bundle, which includes 1Password and seven other great apps, for just $49. (This offer ends in four days, so move quick.)