Looking through my pdf collection, it occurs to me that while I enjoy RPGs that are self-contained and don’t need a ton of splats to be playable or feel complete, I definitely went through a stage of picking up a lot of supplements during the height of the d20 craze. Most of those books are now gone, and my supplements for systems such as Castles & Crusades and Pathfinder are few indeed. It takes a lot more to make it on my shelf these days, apparently.
I think that the types of supplements I’ve enjoyed most are collections of magical items. The Encyclopedia Magica, for example, was a tremendous amount of fun, because I could flip to a random page and find something like a Rope of Ladder Enhancement. Perhaps only a small percent of those items ever saw the light of day in one of my campaigns, but the Encyclopedia Magica still ranks up there as one of my favorite supplements.
Equipment guides also seems to find their way to my shelf. Iron Crown’s …And A 10-Foot Pole is still the best equipment supplement I’ve ever used, but the 3.5e Arms & Equipment Guide found its way to my shelf early on. So did Palladium’s weapon books. I don’t know why, but long lists of weapons, trade goods, daily necessities and the like have always held a bit of a fascination for me.
Bestiaries? Not so much. I had the requisite Monster Manual, of course, but I’ve never needed a lot of baddies. I usually end up repurposing the ones in the main monster book, or creating/generating my own terrible creations. That’s not to say I don’t enjoy a lovely mix of terrible beasties, but I don’t seem to support it with the wallet, either.
Other items like campaign settings (love the map, enjoy perusing the settings, but sort of have my own thing going on, unless it’s some tremendous like Hellfrost), new classes/feats/races (if it’s too exotic it probably won’t get used; if it’s another kind of elf, I don’t care), and spellbooks (I don’t play a lot of magic users, and new spells usually need to be at least nominally checked out before being allowed) have seen spot purchasing here and there.
Really, a format now largely lacking that I miss are the old Rolemaster Companions. They might have a few new races, a couple new classes, new spell lists, skills, etc., etc., all in one tome. The closest thing to this I’ve seen recently is the Pathfinder Advanced Player’s Guide, but you also want to be sure with this sort of product that you aren’t superseding or causing tons of rules updates in the original core product.
Of course, there are also GURPS supplements such as Age of Napoleon or Scarlet Pimpernel, I don’t use the GURPS system, but their sourcebooks are golden nonetheless.
So what about you? What sorts of supplements have you favored over the years?