On January 15, the National Park Service will allow entrance to more than 400 national parks (Joshua Tree National Park pictured) for free in celebration of Martin Luther King, Jr. Day. That's a savings of up to $30 (at Grand Canyon National Park, the most expensive national park) -- or perhaps even more, if the National Park Service's proposal goes into effect.

Note: Admission will also be free on April 21 (first day of National Park Week), September 22 (National Public Lands Day), and November 11 (Veterans Day). Admission to most national parks is usually free; click here for a list of parks that offer free admission these days.