Manual of the Planes might also qualify, and I remember the rules were pretty freaky at times... The alternative Prime Material Plane thing sounded neat, as did the Magical, Physical, and Time Factors of each plane. Though, if I got put on a plane with a Magical Factor that sucked and I was like, I don't know, a spellcaster, I'd probably hyperventilate IRL. Sounds bad, man.
Unearthed Arcana might also qualify, there were a lot more "neat" spells thrown in there.
Six days after mine. O happy year this will be! :D!
And yeah, the demi-human level cap was pretty much fluff made into a game mechanic. I do kind of like how one race having a low cap in one class sort of reflected on their race's (or I think gender, in the case of drow) tendencies towards that class...at least to me.
Books, I miss you. I wish I'd put that extra pair of clothing in storage and not you. ;___;