Multiple Passwords for Better Protection

Why?

Even if you have a good password for your computer or an online service, it can still be compromised by physical (someone watches you) or technical (key logger) means.

How?

Build a mechanism that allows you to specify two or more passwords for the same account (making sure all of them are good and hard to crack.) Each time you can use any of them except the last one you used. This way if you have been compromised the password thief will still not be able to log in. If you use 3 or more passwords, it will be even safer.