Most rabies vaccines are good for three years. This was according to a vet I had in Albuquerque. My other cat Irene, who passed, had a reaction to the rabies vaccine and had to have a growth removed from the injection site (paid for by the vaccine company). This type of reaction is very rare and in those types of cases it is advised to vaccinate as rarely as possible.
However, Larry is correct that most states/locations require yearly rabies vaccinations to register your cat. That being said, the only place I've ever registered my cat is where I live now and that was only because I started allowing him outside.
Edwin actually got to have two rabies shots last year since he bit a bat (inside the house). I don't think the bat bit him, but it was obvious that he had been chewing on the poor bat. Since I was able to capture the bat, the DNR picked it up to test it for rabies. The test came back negative for rabies. It was good to know, but sad that the bat had to be killed just because my cat loves to chew on bats.
Edwin went after another bat just the other night. I've told him no more bats, but he just won't listen.