Yes, there are several. Not sure what part of town you will be in, but I like the Goodwill in the shopping center at the corner of Jones Bridge and Abbotts Bridge. It's relatively new, large and clean. (This may technically be in Johns Creek, but it's close to Alpharetta.)
On the other side of town, there are the stores the PP have mentioned and a few more, all located on Alpharetta Hwy/Hwy 9. Going northbound, they are all located on the right side of the road -- Value Village, [one I haven't been in so I can't remember the name], Park Ave Thrift, and Goodwill.
HTH!