from Orlando, you'll be able to do easy boat dives off Daytona Beach.
a longer drive down to Jupiter will get you very, very nice
coral reef diving.
for fresh water diving, you can try Blue Spring (at Orange City) and
Paradise Spring (near Ocala).
a little more driving will take you to Crystal River. you can snorkel with
the manatees in winter, and dive King Spring year-round (along with
other smaller springs in the Bay).
cerich makes a great point. you are in one of the prime cave diving
areas in the world. you can head up to High Springs and do cavern and
cave training and enjoy all the caves in the area.