A "must see" in Guatemala City is the National Ethnology and Archaeology Museum, usually just called The Archaeology Museum. It contains the most important collection of Mayan artifacts in the country. Some of the items are in remarkably good condition. I don't have any pictures of the jade exhibit, but it is VERY impressive and has a beautiful collection of earrings, bracelets, and masks.
There is a very impressive scale model of the Mayan archaeological
site Tikal, which is located in the northern part of the country.