There are all sorts of methods of authentication (making sure someone is who they say they are). Passwords are one way. The problem there is that people usually a) choose something basic or b) choose something complex and then write it down.
I think in the future that you may see more biometric (body measurement) devices. These types of devices go back to the 1930's, believe it or not.
Here's a site with information on all sorts of biometric devices. Some look rather strange (measuring the time spacing of typed words??):
http://ctl.ncsc.dni.us/biomet%20web/BMIndividuals.html
