One of my all time favorite books in the GAZ series and maybe even the entire Basic D&D line is out today at DnDClassics.com.
GAZ 3 The Principalities of Glantri.
Even today I go back to this book. I loved Glantri and made it "my" country for years. The School of Magic, the Necromancers, the Witches and more. Just a treasure trove of great stuff.
I recently picked up a "new" copy of the dead tree version, but having the PDF will be great.