The Outside Magazine team assembled what they describe as the ultimate guide to the National Parks. It's pretty impressive!
http://bit.ly/National_Parks_Plan_A_Trip
Worth noting that, once you attain the age of 62, you can buy a Senior Pass, for $10, that is a lifetime pass. If you are a geezer ( like me) who enjoys the many varied National Parks, it's a great deal.
Truly one of the great bargains! I use mine to travel to the Great Falls National Park which is 10 minutes from the house...nothing like doing a conference call while looking at the Potomac River!