Yep, putting the D&D Expert Rules into a clean PDF is certainly big news. For a grand total of $10 you can get your Basic and Expert D&D rules and have years of playing ahead of you with original (not cloned rules).
See, it's times like this that I regret starting my RPG experience with AD&D and mistakenly thinking of B/X as D&D "rules for kids". It took me years to get past that idea.
Monster Manual II - This was the the third of the AD&D monster books, and probably the only one that stuck to the actual AD&D rules (MM1 was released before the AD&D rules were completed, and often feels like a D&D book to me. As for the Fiend Folio, those wacky Brits produced a lovely wacky monster book). I still love the cover even today.
The Wilderness Survival Guide and the Dungeoneer's Survival Guide introduced Non-Weapon Proficiencies to core AD&D (they made their first appearance in Oriental Adventures). Aside from that, I don't recall getting much use from them. Maybe someone else did. The came out on the tail end of AD&D 1e, and I remember them being sold at a steep discount at the Complete Strategist in Manhattan when 2e released.