I'd like to cast my vote for the San Felasco State Park, which is just north of Gainesville, and just south of Alachua.
There are a couple of entrances. The easiest to find is on 441, a few miles south of Alachua. Easy access from I-75.
http://www.floridastateparks.org/san...ck/default.cfm
Will try to post some photos shortly. A nice variety of terrain. Well maintained bike and horse trails, the main activity of this park.