One of the most beautiful places on earth. I think we've gone there 3 of the 4 past summers and we're probably going again this year.
We plan to stay here:
http://www.monumentvalleyview.com/
It was under construction last summer. I think it just opened in January. It's one of two hotels near Monument Valley (Gouldings is the other), and the only one where you can actually see the valley from your room. It's attached to the visitor's center. It should be spectacular.
Otherwise, you're staying in a Motel 6 30 miles away in Kayenta, dodging the stray dogs outside McDonalds.
Don't make the mistake of thinking you can see it from the highway. You can't. You have to pay the fee to the Indians and drive down into the valley on a dirt road, or take a tour. The road is rough but we've done it in a minivan with no problems. The tours are supposed to be tremendous - they take you places you're not allowed to drive to - but dust is a major problem riding in an open jeep on dirt roads.
One of my favorite things in the area is the local radio station. They play old country (think Patsy Cline and Ferlin Husky), CNN Headline News, and traditional Navajo music, with DJs that speak Navajo. It's a trip.
While you're in the area I highly recommend Canyon de Chelly, about 80 miles south of Monument Valley. It's in the middle of Navajo country, for my money it's far neater than the Grand Canyon, and absolutely nobody goes there. It'll be you, some German tourists, and a few Navajos selling their artwork. It's pretty spectacular.
About 100 miles west is Antelope Canyon, just outside Page. Do a Google image search for Antelope Canyon. It'll knock you on your ass.
3Bags is right about Zion. And Bryce Canyon is pretty amazing too.
Have fun. It's one of my favorite parts of the country.