The 'must see' parks in Orlando are The Magic Kingdom, Epcot, Disney MGM Studios, Disney Animal Kingdom, Universal Studios, and Islands of Adventure theme park.
Trips to Kennedy Space Centre take a full day and are good for adults and teenagers.
During previous visits we have also been to Sea World and Busch Gardens (if you have limited time, recommend that you drop Busch Gardens).
Also worth a visit if you have time is Cypress Gardens (the original theme park before Disney and more low key) and Forever Florida (wildlife viewing from a tall wagon).
Quick Tips:
You can avoid the main tourist hordes by getting to the parks early and heading for the far side first. We used an excellent tourist guidebook to show best days to go to the parks and hints and tips on rides (A Brit's guide to Orlando and Disney world by Simon Veness, ISBN 0572026498).
Due to the lower than normal tourist numbers, when we attended there was very little queuing this year.
Don't forget to make a note of where you parked your car in the Theme Park car parks as they all look the same when you get back.
Best Way To Get Around:
We flew into Sandford airport (which is primarily a British Charter flight gateway) from Birmingham, UK, and collected our hire car.
Be sure to be firm with the car hire company clerk to ensure that you don't get pushed into unwanted extras, like car upgrades that you don't need.
Don't forget that in an automatic car you have to put it in Park first or you won't be able to take the keys out of the ignition (this can be frustrating if you don't know!).