I'm going to be in Marietta next month and will be on a pretty tight budget. I'm looking for the best free and inexpensive things to check out! I love the outdoors, art, museums, you name it. Thanks!
There is a free concert on July 31st and the fireworks on the 4th at the Marietta Square: http://www.mariettaga.gov/city/residents/parks/specialevents/concertseries
There are free movies not too far from Marietta if you have a car.
Tons of festivals in Atlanta.
I also think it's fun to buy a raft at Wall Mart and Shoot the Hooch. If you don't have 2 cars you can take a shuttle from one of the river companies.