Definitely don't miss the bus tour...it's the highlight of the day, IMO. First stop is the viewing tower, where you will be able to see the Space Shuttle launch complex. If there's a shuttle on the pad at the time, the view is amazing! The next stop, the Saturn V center, is simply amazing. You'll be taken into a mock-up of the old mission control room, where they'll simulate the launch of Apollo 11...really cool! Then the doors open up and right in front of you is one of the Saturn V rockets, stretching the length of the building. There are incredible exhibits and summaries of all the Apollo missions, as well as a food court and gift shop. You then board the bus that takes you back to the Visitor Complex. In between all of that, you'll get great information on all the "goings on" of KSC and NASA, an up-close look at the VAB (Vehicle Assembly Building), and even a nature tour (tons of alligators in the canals, and a bald eagle nest, too!).
It's well worth the time and money...plan on spending the entire day!