I also recommend Shark Valley....great place!
Another great place is Cypress Bend at Fakahatchee Preserve
Check this:
http://www.friendsoffakahatchee.org/boardwalk.php
http://www.friendsoffakahatchee.org/
After this (on a Sunday) visit "Stan's Idle Hour" in Goodland, wich is nearby.
http://www.stansidlehour.net/
Stan's "Sunday Show" starts every Sunday at 1 pm. with a live country band and finishes at 6 or 7 pm., depending on the crowd. Join the locals and tourists as they eat, drink and dance! Stan sings and tells jokes, and around 4:30 pm, you can hear the 'guest singers'! It's an afternoon of fun and people watching!