This week: Google Authenticator is available for both android and iphone. It turns your smartphone into a key fob, allowing for you to use 2 factor authentication to get into a variety of applications.
Be sure to read up on each individual application's method to disable 2 factor authentication or how to use a functional failsafe just in case you lose your phone or it is destroyed by a toddler.
I currently use it for my multiple Gmail accounts and LastPass.
Google Authenticator has made securing my Gmail accounts easy.