Yora
Legend
Caverns of Thracia and Dark Tower get all the glory, but Savage Frontier probably had the biggest and longest lasting impact by far.
The North in the original Grey Box Campaign Set is extremely sparse and broad strokes. Waterdeep had been covered before, but to my kowledge there really wasn't any specific content for the rest of the region before Savage Frontier. And since WotC took over, it's been pretty much the core region of Forgotten Realms, now with just a bit of Baldur's Gate and it's suburbs added for good measure.
And even on its own merits, The Savage Frontier is really good. A ludicrous density of actually useful content for running campaigns on such a tiny page count.
The North in the original Grey Box Campaign Set is extremely sparse and broad strokes. Waterdeep had been covered before, but to my kowledge there really wasn't any specific content for the rest of the region before Savage Frontier. And since WotC took over, it's been pretty much the core region of Forgotten Realms, now with just a bit of Baldur's Gate and it's suburbs added for good measure.
And even on its own merits, The Savage Frontier is really good. A ludicrous density of actually useful content for running campaigns on such a tiny page count.