Karen, we (me, DH, DS12 and DS14) visited the Grand Canyon last July, and words just cannot describe it. I had tears in my eyes, it was just so magnificent!
We stayed 2 nights at the Kachina Lodge, had dinner at El Tovar both nights. You'll love it! Have you reserved the mule ride to the bottom of the canyon? We didn't, for 2 reasons: (1) none of us had ever ridden a horse before and I figured 4 hours on a mule was a bit too much for the first time; and (2) there's a weight limit of 200 lbs fully clothed and DH weighs 210. Turns out even if we HAD done the mule ride, they had a horrible rain/hail storm the day before we got there and the trail (Bright Angel Trail) that the mules go down was closed because part of it was washed out.
Instead, we walked along the Rim Trail, which took most of the morning. There's a free shuttle bus you can hop on and off at certain stops - we walked a good bit of the trail, then took the shuttle bus to Hermit's Rest and then took the bus all the way back. In the afternoon, we drove to the South Kaibab trail (I think there's a different shuttle out that direction, but for some reason we drove) and hiked part way down. Since it was afternoon and the deeper you go into the canyon the hotter it gets, we didn't go all the way down to the bottom, but we went far enough to get an idea of what it's like to look back up.
One evening we did a jeep tour - I think the name of the company was Grand Canyon Jeep Tours. It went thru the Kaibab National Forest (which surrounds Grand Canyon National Park), and we ended up at a really neat overlook to watch the sunset. There was also a stop at a fire tower where the brave could climb to the top for a spectacular view.
We also did a one-hour horseback trail ride thru part of the Kaibab Forest. The stables are right outside the park entrance, and you go on nice, flat terrain. Perfect for us novice horse-back riders!
You'll get a newspaper with a list of all the ranger tours - we didn't do any, mainly because we were never in the right place when the tours were due to start. Some of the tours sounded really neat.
Be sure to pack the right clothes - we were there in July, and the nights/early mornings were COLD, but the afternoons were HOT.
Oh, be sure to get up early to watch the sunrise. And watch for the elk - they come to graze on the grass around the El Tovar early in the morning.
If you want any more info, let me know. I'd love to go back again some day, maybe in spring or fall. It's truly magnificent.
) to take "straight down" video. He was freaking me out to no end. I stayed on the path, which even that was too close for comfort with no barricade between me and the great hole. 
