If you drive the 73, 133, 241, or 261 toll roads in Southern California, you now need a transponder or sign up for an account. Tolls will no longer be collected on the roads. Signing up is very easy to do.
Go to https://www.thetollroads.com/
Update: The toll booths will not be removed until May 2014 but you can sign up now for an account and get a $10 credit for doing so or order a transponder.