The Grand Canyon was absolutely breathtaking. I took pictures of the rock formations from many angles, and it never got boring. We went early one day (the parking lots are full by 10 AM, and there is a waiting line to get into the park) and spent the day taking the shuttle bus to Yaki Point and the South Kaibab Trailhead and walking the Rim Trail, and then taking the car to Desert View. We visited almost every available overview. The next day, we took the train from Williams to the park train station and spent the day exploring Grand Canyon Village and the Rim Trail in that area. Wowee.
Petrified Forest National Park is split by I-40, and from that highway you hardly realize what you are missing as you whiz by. Not only are there plenty of petrified trees (although early tourists and greedy people destroyed much of them), but it is also part of the Painted Desert and the colorful Badlands there. Another area of spectacular scenery.