We subscribed to Trade Coffee for about 8 months and they sent us a totally new bag from a different roaster every week. We played around with it a lot, many different kinds and roasts of coffee, and found one roaster in Atlanta we really like. You rate each coffee as you try them and they adjust what to send you next week. You can read descriptions of each coffee on their site and pick what order things come in.
It's perfect for when you want to have a broad selection of coffee over time.
My only warning is Trade doesn't really do dark, dark roasts. My taste pallette falls all the way at the end of their range and their rating scale is a little confusing so it took me a couple conversations with their customer service department to get my account set to only send dark roasts.