This one has an excelent reputation which is fully deserved. While being a sandbox campaign setting on the surface, it actually is a very useful model for the creation of campaign settings in general, which should be very useful for all GMs. Even if you're using an already existing setting, it's a great resource to not just create small locations, but to actually come up with groups of people to encounter, who are not just traveling on the road, but have their own motives and problems.
Recommended without reservations.
[5 of 5 Stars!]