National parks are already a great deal for families traveling on a budget. For four days in 2010, they'll be an even better deal when the parks waive admission and other fees.

The National Park Service will offer free admission to more than 100 national parks on the weekend of August 14-15 and again on September 25 (Public Lands Day) and November 11 (Veterans Day). Fees for commercial tours and transportation also will be waived on those days, but visitors still will be charged for reservations, camping and concessions. Visitors also may be charged fees by non-Parks businesses, although some vendors are offering deals and discounts on boat trips, t-shirts and lodging in conjunction with the free admission days.

Find a list of participating parks here. Some parks of note are the Grand Canyon, Joshua Tree, Yosemite National Park, Yellowstone National Park, Death Valley, Fort Sumter National Monument, Mount Rainier National Park and Devil’s Tower National Monument.