Occult Lore: More new magic systems than you can toss a three-legged cat at. Good art, good writing, inovative ideas (for the most part). Hard cover and fairly meaty, but still a good price.
The Book of the Rightious: More divine goodness than you can chuck that cat's missing leg at. VERY meaty for a good price.
Mongoose' entire Encyclopedia Divine/Arcane series. These guys rock, and are not too hung-up on the "norm" to treat some very interesting ground with magic. From an excelent portral of necromancy, to an amazingly tasteful treatment of Demon Summoning, to balanced war mages, to fey-granted powers, to an entire book dedicated to constructs, to a freeform magic system, to the best d20 shaman to date and more, these guys are on the ball. I'm going to count these as one product because individualy each one is about the size of a chapter in a normal book.
WoT: This book is what the 3E core rules should have been, plus a MM. Slick, great art, good writing, and the best treatment of prestige classes I've seen (With one noteable exception each side, prestige classes and core classes are very well devided, with each being more or less what they should be). Also, an amazingly cool magic system that is still very easy to pick up on if you know normal vancian magic.
Oriental Adventures/Rokugan: I can't decided between these... it's a tie. They both rock equaly, just in different ways. The Courtier class in Rokugan is almost enough in and of itself to push it over the line, but some great prestige classes and rules presented in OA and not Rokugan (Such as Iajutsu, the Iajutsu master, the Blade Dancer, etc) keep it balanced...