Operating Gateman houses and whistle houses are always good. The newspaper stand is a favorite as well.
I use inexpensive doorbell buttons to operate them. The buttons are big and don't take much force to work, two things that make them more friendly for kids of all ages. Just avoid the lighted doorbell buttons, they let a little current through all the time which can cause problems.
As to operating cars I always loved missle launchers as a kid but they do tend to cause some havoc!