Don't forget this awesome offer from the National Parks System -- Free Annual Pass for U.S. Military
Available to U.S. military members and dependents in the Army, Navy, Air Force, Marines and Coast Guard and also, Reserve and National Guard members.
Must be obtained in person at a Federal recreation site by showing a Common Access Card (CAC) or Military ID (Form 1173).
Frequently Asked Questions about the Annual Pass for U.S. Military
Go here to learn more.