I can't count how many I have. I have loads of books in the Kalamar line, the Scarred Lands line, the Bluffside line, most of the Necromancer Games adventures, several Green Ronin sourcebooks, and a number of ohter setting books, including Nyambe, Codex of Erde, Arcana Unearthed etc.
I have a number of other adventures by miscellaneous publishers, including Monkeygod Enterprises and Troll Lord Games.
I have many many PDFs, including many Malhavoc ones and ones by miscellanous PDF publishers.
This excludes my WotC books, which include most books since the 3.5 revision.
Products most used: It varies tremendously on whether I DM or not and what sort of campaign it is. My current DM doens't allow unofficial stuff, so d20 sourcebooks are only good for fluff inspiration for my character.
Really, I think I have a lot of books which primarily sit on the shelf, sometimes get read, but could see immense use if I run the right sort of campaign, or play in one.
I hope to run an exalted style campaing in hte future. If I do, I'd use the following heavily: BoED, BoVD, BoHM I & II, Book of the Righteous. Probably Manual of the Planes, and I'd choose some suitable adventures as I like to use published adventures. Finally, I"d use one of the settings I have.
I recently ran the modules X4-5 in conversion and set them in Kalamar. Tomb of Horrors saw extensive use, as did the Miniatures Handbook, Lords of Darkness, and some others.