• Coral Gables: Beautiful tree-lined streets, interesting scenery everywhere... this is easily the most beautiful place in South Florida.
• Coconut Grove: Also equipped with nice tree-lined streets, and some odd hills and ridges. Alongside Main Highway is a beautiful wide paved bike path, which winds on through the roots of banyan trees for about a mile as it goes on into the area around Cocowalk. After somehow finding your way through the sidewalk cafes without killing anyone, go downhill to the east and north on Bayshore Drive. The park you'll come to after Coconut Grove Convention Center is worth checking out; it has a neat boardwalk where you can go out over the bay. A word of advice: Don't follow Ingrham Highway where it splits off of Douglas Road, unless you happen to like having cars and the occasional NABI 40LFW flying past you at 40 miles per hour on a two-lane road with no possible means of escape.
• Kendale Lakes: For those of us out in the western suburban sprawl, this area is a nice change from the usual smoggy, bare, concrete moonscape. North of Kendall Drive, and west of 137th Avenue, there's a very large area with miles of wide, winding, and usually empty roads going around a golf course. Tree cover is present. There is a similar area located south of Miller Square at Miller Road and 137th.
• Horse Country: Between Sunset Drive and Bird Road, and starting just west of the Florida's Turnpike, you can ride through Horse Country without finding too much traffic.
• Key Biscayne: Niftiness abounds once you get onto the island, from the natural hammock of Crandon Park, to the multi-million dollar mansions of Mashta Island. The Rickenbacker Causeway is a long ride, but features some neat stuff like a bridge that just about pokes into the heavens.
• Old Cutler Road: From where it begins at the circle with Sunset Drive, and all the way down to Snapper Creek, a beautiful trail runs under massive oaks. The trail back through Matheson Hammock park's mangroves is worth checking out, but don't stop on it too long unless you like being eaten alive by mosquitoes.
• Oleta River State Park: Located in North Miami Beach, and equipped with a variety of mountain biking trails ranging from the tame to the technical (read: AAUGH!)

I'm sure there are also a lot of other nifty places to ride that I just haven't discovered yet...