well:
core books
some rules clarification etc from the spalts, one character going for a PrC.
Oriental adventures for new monk stuff and some feats and martial arts stuff
Used a monster from the BoVD last time.
Used soemthing out of Monsters of Faerun too.
Used some spells and some rules from MAgic of Faerun
i've used some rules out of tournaments, fairs and taverns, some npcs out of hammer and helm, ripped a map out of stronghold builders guidebook
so i guess 75% has seen some use, but only the core rules, OA and some splatt stuff gets used regularly... and the rules stuff is like "oh, lets play like that" then never looked at again...