This is a good idea. Here's a few from my area.
Central Florida Trails
I've biked both of these and they are pretty nice trails.
East Central area: Cady Way Trail - 3 1/2 miles. This is an asphalt trail that runs behind the old Navy base. Most of the trail can be walked on the side in the grass and dirt. There are lots of bikes and skaters on this one. Trail Runs from behind the Fashion Square Mall off of Harrington Ave and ends at Cady Way Park.
Watch out for horses and their 'droppings' on this one
West Orange County: West Orange Trail - 19 miles, again, asphalt but most can be traversted on the side in the grass. Runs from Hwy 441 and 435 to Hwy 50 and hwy 91.
There are several other trails in central florida that would suffice for training. A list can be found here
More Trails