Acorn Valley, Sandpiper, and Walnut Ridge have great trails.
I-35/80: Take Exit 127 to Highway 141 N. Take Highway 141 N approximately 6 miles to exit 148 which is NW Saylorville Drive or Hwy 415. NW Saylorville Drive will lead into the lake area.
http://www.tripleblaze.com/trail.php?c=3&i=6252