I love books and I happened to marry a woman with the same passion, so between us we have quite a few; I have lost count, but somewhere between 3 and 4 thousand. I used to have them all cataloged, but lost the “list” during a computer upgrade some time back.
I am using Delicious Library 2 to catalog our books, absolute the best program to catalog your books, movies, music and you name it. It can sync with your iPhone/Touch, so now I will never get in a situation where I have bought the same book twice, because it sounded real nice in the book store, but I could not remember if I had it already – maybe I’m just getting old, but it has actually happened a few times.
I still have a long way to go, but the ever expanding list can always be viewed here (or here if you have an iPhone).