Planning info for all U.S. parks (Note: This site requires patience to navigate, but it's worth the effort.)
The National Park Service's search tool lets you locate parks by state, name, activity and topics like Civil War, American Presidents, coral reefs, etc.
You might find these helpful in planning your next road trip!
Just about every National Park in the US has at least one web cam, but you need to navigate to each park's web site to locate them. Here are some representative samples:
View of the woodlands behind the Foothills Visitor Center
View of the peak & Paradise Valley
View of western boundary
View of Viginia's Shenandoah Valley
Badlands National Park, Mt. Rushmore, Crazy Horse Memorial, and the historic town of Deadwood
View from Yavapai Point with current weather & air quality info
Live web cam showing a terrific view of Half Dome
Live web cam view of "Old Faithful" Geyser
Live web cam view of the Many Glacier