This post I intend not to sound too sycophantic & of course these are absolutely the correct opinions no rational person could possibly disagree with them.
I'm going to give a top 10:
1. Master Atlas 3rd ed.: Though not everything in the 2nd ed MA made it into the 3rd ed. tome it still is the first I turn to when searching for info. The 3rd ed. MA is better organized & contains more information overall from the extended Timeline to the longer more in depth descriptions of the non-core continents. The 1st ed. MA doesn't compare to the 3rd & 2nd editions, except I find some of the art less polished yet more evocative. I think the art in the 3rd ed. MA is the weakest of all the MA's I greatly prefer pen & pencil drawings to computer generated art.
2. Emer boxed set: Only just inches out the other supplements because of the Atlas addendum. Has so many iconic entries especially the entries on the "Guardian Mind", The Ark of Worlds & the Book of Gates. It has an excellent overview of Emer itself, including information about SW Emer that can't be found elsewhere.
3. Jaiman Land of Twilight: If Emer did not have the Atlas Addendum this would be the #2 supplement. Jaiman has the most interesting setting including Lorgalis, the Priests Arnak, the Phoenix Crown, & Sulthon Ni'Shaang. It's like central Europe there's too much history to ignore.
4. Haalkitaine: The Empire of Rhakhaan's place in Jaiman is central both geographically & historically to Jaiman. It also gives some context to how the various powers in Jaiman play out their conflicts. I refer to its weather generation system constantly.
5. Powers of Light & Darkness: Comprehensive. I don't know how I could run a SW campaign without it. If I was rating these purely by how much I enjoyed reading them this would be my #2. My only complaint is I wish it had more about the Alliance & some info that appeared here appears elsewhere, but having it organized into one place. The spell addendum which I finally found would push this over to #2 if it had been included with the softback. Lastly the binding on mine is shoddy don't know if it's a defect from the print run or just the one copy.
6. Xa-ar & NW Saralis: This may indeed be Mr. Amthor's best work buying it made me more fanatical about running the SW. The first half is an excellent source book & the second half is the best adventure for SW I've ever read. This is my favorite I hope the Wuliris Supplement is similar.
7. Emer III: It's always a good sign when one finds the quality of an author's writing gets better as time goes on. I personally thought this area was going to be the dullest part of the Emer series, especially compared to Emer II (Namar-Tol & the Lankan Empire), but I would start a campaign here if I wasn't still running my Jaiman based campaign.
8. Emer II: Could have been 3 or 4 times larger in other words moar of this. Luckily there seems to be more in the works.
9. Eidolon: Currents & trade routes alone make this a must have. The great city of Sel-Kai and sky ships are the meat of this supplement. I like the idea of an expansion of this.
10. The Iron Wind: The first supplement for SW it set the tone, introducing the Priests Arnak, The Dragonlords, The Messengers, The Navigators & the Loremasters. Even though they are expanded upon in many later works they remain in essence the same.
Emer I, the 2nd & 4th ed. MA, The Cloudlords of Tanara (both versions) both are excellent additions. The only non-Amthorian work that I consider on par is Vog Mur, but it lacks the Amthorian touch.
Demons of the Burning Night, Gethaena, Bladestorm, & Quellborne are the only others i like, but for the most part I ignore them they seem out of place in SW. Quellborne especially seems like it belongs in Greyhawk or the Forgotten Realm.
Norek gets praise, but i never liked it & the others Cyclops Vale, Isle of the Oracle, Tales from the Loremasters I & II, etc. were not worthy additions. They seem like locations pulled from very derivative homebrewed settings. They completely diluted the setting & I for one am glad they are not considered cannon by TKA.