I have been to Homosassa and agree it is superior for viewing as opposed to city areas or power discharge areas. However, if you do not want to wander so far west there is EXCELLENT viewing of manatees in the Central Florida area about 45 minutes north of the WDW's mousetrap. Blue Spring State Park has easy access on a boardwalk and much viewing. Swimming with the manatees is prohibited. Protected species... yadda yadda... which translates to: "tastes just like chicken"

Nice video to watch manatee frolicking (as best they can):
http://www.bluespringflorida.com/

Official state park website:
http://www.floridastateparks.org/bluespring/default.cfm

enjoy.