If you're a car enthusiast, this could be a big (free) weeekend...
The exhibit at the High Museum, Dream Cars, is incredible.
http://www.high.org/
Admission is free this weekend on Saturday for Fulton County residents (limited supply of tickets) and on Saturday and Sunday for Bank of America customers.
Caffine and Octane is a free drive-in auto show held off Windward Parkway in Alpharetta the first Sunday of every month.
http://www.caffeineandoctane.com/
Dozens (maybe hundreds) of spectacular/customized vehicles show up to be gawked at ranging from (at my last visit) a line-up of cars from the 30's and 40's to McLaren, Bugatti, Aston Martin, etc.
It runs from 8 to 11am but consider getting there early as parking in the surrounding lots fills up quickly.