I use the SRD for Monsters (looking thru the 3.5 MM I didn't find it worth buying as the layout sucked as much as it did in the 3.0 one) and for DMG stuff (another generally useless book in my estimation).
I didn't do an exact count, but I'm fairly sure I hit 100+.
I've got practically every sourcebook and adventure released by WotC, all the issues of Dungeon and Dragon, D&D and DM for Dummies, as well as the basic sets, all the Dungeon Tiles sets, plenty of minis and some third-party stuff as well.
I haven't counted my physical books, but I strongly suspect that they're 100+, especially given the way magazines are counted for this poll. If I add in PDFs, then that number skyrockets dramatically.