Over two dozen. A mix of World Works terrain, old D&D ESDs, and 3e supplements.
Of these the ones that see the most use are Adventure Design Kit(TSR ESD The Chases sheet actually works better with 3.x than it did with 1e), Librum Equitus Compliled (I have sent several customers happily after this book), Book of Templates Deluxe, World Works' Dungeon Works (I have Gothic Realms, but I printed up way too much Dungeon Works in my early enthusiasm, enthusiasim which fortunately is still present...), WW Interior Works: Castles & Keeps (especially the stairs), and Village Works (again, I have sent at least two customers questing after WW material) and while I haven't used it much yet I have read A Magical Medieval Society from cover to cover.
In the Saddle has been used a bit as well, and I amusing Campaign Planner retroactively to suggest reading material for the players in my campaign. Elements of Magic is waiting for a later campaign, just too different for my current players.
The only PDF purchases I am at all unhappy with are some of the Cheep sets, compared to World Works they just don't measure up.
The Auld Grump, there are a lot more, but those are particularly worth mentioning.