Similar to Myrddin, I collect books, though I've read all of mine. I read them immediately. I have several on several topics: Anthropological studies, Theology, mythology, paranormal, horror, romance, mystery. I love books! I can't wait until I have enough to have the excuse to build a library in my home!
When I was little I collected rocks-I still have some of them sitting on my bookcase. My son has since taken up collecting rocks and bringing them to me as gifts so now I have those as well.