When my wife and I went to Rocky Mountain National Park in Colorado last summer we picked up a very cool postcard book featuring the poster artwork the Works Progress Administration commissioned in the 1930's to promote the parks. They're all beautiful but here are a few of my favorites.
I think my favorite one has to be this beauty from Sequoia National Park.
I highly recommend this set if you're at any of the National Parks. They're a great souvenir.