I really like riding in the Lakewood Ranch area. Go to the Villagebikes.com site mentioned above and click on local rides.
Click on the Linger Lodge Rd ride.
The map will show a nice ride but the whole area offers many side routes and circuits you can devise rides on your own.
What is really great is Lakewood Ranch is a planned community and its own township, so most all of the roads are newer, smooth and feature wide cycling lanes Best of all, low traffic volumes as this is a very upscale residential community.
Many side routes offer winding curving roadways to limit the vehicular speeds through high end real estate planned developments.
Look at google maps, I find it easy to come up with a 40 mile looping ride.
Some of my favorite roads are Lorraine Rd, Hidden River Rd, Masters Rd winding through the golf courses and country club. Just so little traffic especially on the weekends.
There are plenty of business and strip mall parking lots to start your ride from if you can't easily ride there.
I am fortunate to take a ride through the Meadows, another upscale residential area on my way to Lakewood Ranch.
There are all kinds of places to stop and refill your gatorade on hot summer rides.
You will see other serious riders and groups of riders in this area.
While its not quite as scenic as Longboat Key it is so much easier traffic wise as long as you stay off University Ave. But even University has a decent sidewalk if you want to avoid a short stretch on a higher speed artery.
Nevertheless I cruise by areas like lake Osprey and see sandhill cranes, turtles, hawks, gators, saw a fox, an eagle, once almost ran over a rattlesnake sunning in the road, so there is some nice nature viewing too.