Aside from renting a car to make the seven-hour drive, Tikal can be reached from Guatemala City by plane, bus, or private shuttle, the choice coming down to your time constraints and budget. It's a short 45-minute flight, but will probably cost over $200 round trio. Buses are $55 one way and can take up to 9 hours with stops. The cost of a private shuttle will fall somewhere in between depending on the amount of people, and will obviously be a little faster and more comfortable than the bus.
Regardless of how you get there, you're in for a real treat when you arrive:
The Northern Acropolis, part of the Great Plaza at Tikal
Great Plaza at Tikal
One of the Twin Pyramids at Tikal
Part of the Plaza of the Seven Temples
Ground view of the Northern Acropolis
[Photos: Will McGough]