I'm up in mount dora, used to live in Orlando. Not much in the city or immediate area, you'll have to drive some. There are some trails out in brevard county if your on the east side of town..
Ocala really isn't too far and there is a little bit of everything. Lakes, trails, sand, mud, hills... great for camping and getting away for a few hours. They are redoing most of the roads where you don't even need 4wd... kinda sucks but makes you feel more comfortable going deeper into the forest alone to find the good places.
Its also nice to know your not going to be trespassing. I work right next to a huge place in Lake Mary where people use to camp and ride dirt bikes but there are signs everywhere to not trespass and if your seen they will call the cops. Most of the little places in or around Orlando are like that nowadays.