One of the coolest wildlife encounters in the USA, you can snorkel with manatees near Crystal River, Florida. The Homosassa Springs Wildlife State Park is the home to many manatees, including babies, and tours go out frequently.
Donning a wetsuit and snorkel gear, you can float in these shallow waters and wait to see if the manatees approach you. Often they will get close enough to brush up against you (for the protection of the animals, wait for them to swim to you rather than the other way around). The waters are relatively clear providing good visability and this is a wonderful outdoor activity for your next vacation.
Crystal River isn't far from Tampa or Orlando, so add it on as a day trip or overnight next time you're headed to the beach or theme parks.