Tikal Tour of the Mayan Ruins, Guatemala

I wouldn't agree that you need to take an organised tour of guatemala. Just brush up on the old spanish and get a good guide book and you will soon find out what is worth checking out.
Here are some posts about guatemala

http://landed.at/best-travel-blogs/282-tikal-lost-civilisation

and here is an excerpt from the top places to go backpacking in the world

http://landed.at/best-travel-blogs/24911-10-of-worlds-top-places-to-go-backpacking-part-2

8) Guatemala. Forget the capital of the same name get to Quetzaltenango Huehuetenango Cobán Antigua Guatemala Panajachel Flores and Tikal. It’s a colourful country full of culture just visit the local markets the locals walk miles to bring hamakas (hammocks) too and woollen handbags. Make sure to visit some ruins Tikal the most famous of all. Its buzzing with backpackers because life here for the backpacker is perhaps as cheap as anywhere. Then there is the old colonial city of Antigua my mate Billy runs one of the best bars in the world there so go say hello ! It’s Monolocos – awesome food and party in this pristine colonial city. Many come here to study Spanish in the numerous schools and it works !