Above: Sunrise on the Gibbon River in Yellowstone National Park
This is a beautiful spot along the Gibbon River, and especially nice at sunrise if you can catch the pink sky and morning mist.
Even better, it's convenient. You'll see a small parking place here - just pull over and follow an unofficial trail along the river. Here is a link to a Google map with the spot - it's a fine photo location for Yellowstone National Park.