I want to backpack in all of the National Parks!  My current list: Grand Canyon, Lassen, and Glacier.  I backpacked in Yellowstone last summer - it was incredible!  Also, I thought it would be crowded and difficult to get permits, but it wasn't.  I think most people stay in their cars and go to the main attractions.  It didn't take long on the trail to get away from the crowds.  I highly recommend backpacking there!