For your convenience, I compiled a directory page featuring some of the top freeware add-on design teams for flight simulator. As I find more groups, I will add them to the list. Consider this phase one with refinement of the directory coming as I have time to update it and add detail about each group.
If you have a favorite freeware group you would like to see on the list, please leave a comment. Of course suggestions and feature requests are always welcome as well!