Late summer and early fall are prime hiking seasons. The air is just a wee bit cooler and the leaves are just starting to turn. If you are at a loss of where to hike I have a great web source for you - TrailLink.com. This site will help you find the best trails for your outdoor recreation of choice, be it: walking, biking, horseback riding or inline skating and more. I would just start with the advanced search because it is more specific, and you can find parks in your state with trails for your activity. You can even search by wheelchair accessibility!
The site is sponsored by the Rails-to-Trails Conservancy initiative (a great program that turns abandoned railroad track into multi-use trails), but the trails listed are not limited to converted railroad trails, they even list some urban bike paths!
So get out there and take a hike!