Player's Handbook II -- there's just a lot of good crunch in this book.
Expanded Psionics Handbook -- perhaps the first decent psionics system in D&D.
Book of Nine Swords -- makes fighter-types competitive with wizard-types for the first time in 3.x, both in terms of utility and having interesting options in play.
Expanded Psionics Handbook -- perhaps the first decent psionics system in D&D.
Book of Nine Swords -- makes fighter-types competitive with wizard-types for the first time in 3.x, both in terms of utility and having interesting options in play.