Many sites require you to use a security question but the options are usually limited and generic (and easy to discover with a bit of Googlefu). Whenever I'm confronted with such a situation, I simply shift the letters in my answer around and make a quick substitution. It's formulaic and easy to remember, but it's different for every site (just like Lifehacker's tips for strong passwords). That way, it's easy to remember the answers but hard(er) for someone else to figure it out.
Just like the password creation method, this isn't necessarily as good as making up your own question — as long as its something only you know the answer to — but it's a good way to seriously beef up the strength of a weak security question.