Holy crap, I marked a lot of those. I admit, I'm a sucker for monster books. As has been pointed out, it's not necessary to have an enormous stack of them, considering the classes and templates and whatnot you can slap onto existing beasties. There's just something about cracking the spine on a brand new book of monsters that does my old heart good, though.
On a related note, I'm finding these past couple of years to have been a really good time for me to be a gamer. Dozens of companies are putting out some quality material for a game I really enjoy. Mind you, there was a fair amount of stuff coming out for AD&D close to 20 years ago - however, there was no way I could buy all the stuff I wanted (or, as I thought at the time, "needed".) Now, however, I'm at a point where I have a good(ish) job, I can support myself, and the quality of third party product is, for the most part, MUCH better than the "Suitable for all fantasy game systems!" stuff put out in the misty days of yore. Ahh, adulthood and 3E - a match made in heaven...Okay, now back to caressing my d20 books.