i went through ProPeten, based in Flores. For a week it cost about US$70... it was very laid-back and quiet, included transporation and room/ sheets/ mosquito netting (!!)... supposedly you had to bring your own food, although we caught a lot of fish and the guys that worked at the biostation made fresh corn tortillas every day... which i deffinitely ate!

i was the only volunteer at the end of July... speaking spanish was a must (no one spoke any english at all)... it was a really awesome experience... i had spent a semester in Chile, and was on my way home, and it was a very interesting contrast. i was supposed to meet a friend (okay... more than a friend!) in Flores (where he was working) but things fell through at the last minute (literally... received an email as i was leaving Peru for Guatemala City). i found ProPeten by chance, and it turned out to be very lucky.

they also do "biotours" that stay in the "nice rooms" at the biostation and include food... i think those are about 2-3 days long. i think they are available in english as well. i would highly recommend ProPeten, as they are a very knowledgable, grassroots organization that does a lot in the community (with environmental education, etc).

as for things in addition to Tikal... there are tours to El Mirador, which is more remote and requires a 2-3 day hike. if you google "El Mirador Guatemala" you'll find a lot, and in Flores you'll see signs in front of all of the tour places in town. tours leave from La Carmelita, and you pretty much have to go with a guide (can be dangerous otherwise, hard to find, etc). most tours cost between US$100 and US$300. there are a number of smaller monuments as well, all within hiking distance (or perhaps jeep trails).

don't make too many plans before you go, as you will find a LOT out when you get there. i pretty much picked up an outdated lonely planet guide book in the Lima, Peru airport and was still more than occupied for 10 days with what i found in Flores. ask around and talk to people (locals and tourists... though there are quite a few locals that will steer you towards their friends).

Los Amigos hostel is a pretty good resource (next to the ProPeten office in Flores). They can also give you advice in Cool Beans (it's owned by a US expat and her Guatemalan husband).

I stayed in Hospedaje Donya Goya's second location, down on Calle Union. Also highly recommended... rooms with a fan, clean private bathroom, and clean sheets for only US$7/night! also, the hammocks on the roof provide beautiful views of the lagoon and jungle. it doesn't include breakfast, but Cool Beans is awesome.

one note about Flores: bring CASH! there are hardly any places to use an ATM/credit card (which about did me in!). US$ are easily exchanged at internet cafes and hotels, Quetzales that you got in the capital will of course be better to use (and a better exchange rate).

have lots of fun!!