I like the trail (paved) around Lake Okeechobee. It's about 100 miles around; no traffic troubles. There are lots of places to camp and fish. You can even camp for free at the Corp of engineer's sites (if you don't mind not having facilities). Try this link for the lake trail and other trails: www.dep.state.fl.us/gwt/guide

I can't speak to riding around Miami, but I think the road to the Keys is hit and miss. There are some good spots to ride and some that would be a little scary, and no other options.

If you go north from Jupiter, though, there is good road riding up the coast all the way to St Augustine. You can run along Intracoastal Waterway--Indian River Rd through St. Lucie, A1A through Vero and Sebastian, Indian River Dr through Cocoa, Rt. 3 through Merrit Island Wildlife Refuge and Canaveral National Seashore, and then A1A off and on again through Daytona to St Augustine.

There's a lot to see on that route: the space center, Daytona Racetrack, Cocoa Beach, St. Augustine. I've never found Miami to be bike friendly. Maybe someone else can throw out some good places to ride down there.