I am a woman traveling alone arriving in Guatemala City late at night. I would appreciate a recommendation for a good hotel and transportation from the airport. Thank you.

The Ciudad Vieja in Zona 10 provides airport transfer and is a very safe, small hotel with decent rates.
Tell them Andrew sent you...
www.ciudadvieja.com

Cheers,
Andrew

Los volcanes a few minutes from airport. Not a fancy place, but they are very attentive pick you up at the airport at any hour, and if you're moving on or have an early flight to Peten, it's the spot.

Use the Marriott
http://marriott.com/property/propertypage/GUADT
It is five minutes form the airport; they have a desk in the airport terminal just after you go through customs; shuttle runs continously.

Thank you all for your suggestions. I will be going to Zacapa the next day for a Habitat for Humanity project. Do you know anything about that area? How safe is the journey to Zacapa?

Unless you are traveling with other "Habitat" folks suggest you arrange for a car/driver. Have you arranged for accommodations while there? Not many "clean & safe" places for single women to stay there. While many folks do travel safely on buses and don't encounter problems remember that single women are "fair game" in Latin America. Best to be safe!

Thank you. Yes, Habitat is arranging for tranfer to Zacapa, but I was curious about the trip and the area. I am only familiar with San Lucas Toliman where I have visited previously.