We're maintaining a list of products which are released for Old-School Essentials using the third party license (see the license here), so that it serves as a repository of all products released specifically for OSE. (Remember, though, that anything released for B/X or other compatible games is usable with Old-School Essentials as well!)
[Update: There's now a category page for Old-School Essentials at DriveThruRPG, so we're no longer maintaining a separate list.]