Web comic xkcd notes that "through 20 years of effort, we've successfully trained everyone to use passwords that are hard for humans to remember, but easy for computers to guess." The comic above makes a compelling (if knowingly imperfect) argument for password length over obscurity, and in response, one developer put together the xkcd password generator. It does what the comic suggests: strings together four random words to create a tough-to-guess password that's easy to remember.
Of course you don't need a generator to do this for you. You can just as easily pull four words out of the air to create your own lengthy but memorable password. Or you can go with one of our tried-and-true favorite methods and create an obscure and memorable password using the first letters of, for example, the lyrics to a song. (For example, a Jackson 5 lover might extract a password from the lyrics "Oh baby give me one more chance to show you that I love you" that looks like obgmomctsytily
.) The benefit of the multi-word method is that the longer your password, the harder it is to crack—which is true for passwords made of both common dictionary words and randomly generated strings of text. Yes, the long, non-dictionary password will be more secure. But good luck remembering a completely randomized 25-character password.
Whatever route your choose for your password, I'd still strongly recommend making said password the master password for a password manager like LastPass, KeePass, or 1Password, then, for all the rest of your logins, use your password managers to spawn long, randomly-generated passwords that are both hard for you to remember and hard for computers to guess. You should only need to remember one password, but you shouldn't use the same password everywhere. That's what password managers do for you: Let you memorize just one strong password and obscure the hell out of the rest. You only need to know the one password; your password manager will fill in your unmemorable passwords for you. Get one, set it up, and use it. We really like LastPass.
Update: As commenter doug_gilbert points out, the four-words method could also work nicely with the shift-to-the-right method.