Encyclopedia Magica (Advanced Dungeons and Dragons), Vol. 4: S-Z + Index

The sheer undertaking of this task — collating all the magic items published over 20 years of D&D and organizing them alphabetically — is simply mind-boggling. You probably won't get that much use out of it in your game, and even if you do you'll never begin to scratch the surface of the material within. But as a reference work, it simply astounds. Volume Four gains an extra half-star for the comprehensive index.