2) B2: Keep of the Borderlands. My copy came with my Moldvay Basic Set. Although, I practically consider it core rules.
3) Deities & Demigods, if that doesn't count as core. (I don't count it as core myself.) Otherwise, I guess its a tie between the World of Greyhawk & Lankhmar: City of Adventure. For WoG, I guess the box set since it has more content, but--nostalgically--the folio will always be the real WoG for me.
4) I played 2e, but only for a few years. I don't remember any of its supplements really standing out in my mind.
3) Deities & Demigods, if that doesn't count as core. (I don't count it as core myself.) Otherwise, I guess its a tie between the World of Greyhawk & Lankhmar: City of Adventure. For WoG, I guess the box set since it has more content, but--nostalgically--the folio will always be the real WoG for me.
4) I played 2e, but only for a few years. I don't remember any of its supplements really standing out in my mind.