Entrance fees will be waived April 17-25 for National Park Week.

Entrance fees will be waived at all 392 national parks April 17-25 for National Park Week.
 
Many parks have organized events, talks, volunteer clean-ups and other projects to encourage the public to visit that week. Details, including a "Find a Park" search option, are online at http://www.nps.gov/npweek/.
 
Events include an invitation to help plant a demonstration garden at Cane River Creole National Historic Park in Louisiana, April 22; a re-creation of Paul Revere's row across Boston Harbor to Charleston, Mass., April 18 beginning at 7 p.m. at Boston National Historic Park; as well as other hikes, wildlife programs and heritage celebrations around the country.
 
A number of parks have special events for kids scheduled for April 24, which is National Junior Ranger Day. Kids who participate in walks, litter pick-ups, and other activities can earn a junior ranger patch.
 
Some park areas and roads are still off-limits to the public this early in the season, and not all services and concessions are open.
 
But a few hotels and other park concessionaires are offering special promotions in conjunction with National Park Week. Offers for coupons, merchandise discounts, freebies and two nights-for-one lodging deals, are listed at http://www.parkpartners.org/Special-Offers-for-2010.html.

thanks for the update ernie, the wife and i were planning to head up to Yosemite on the 24th anyways and this will delay our purchase of the annual pass another month or so =)