Mystery
I enjoy reading mysteries, and that has been the major fare of my reading for close to twenty years. I read other books, but mysteries predominate. And, I like serial mysteries. And, I want to read them in order. In one of my classes, I learned about Fantastic Fiction http://www.fantasticfiction.co.uk/ which gives you information about the author, and helps you by listing the mysteries in order.
I have several series going. This helps in a couple of ways: if I read too many of a series all at once, they all run in together. Secondly, I rarely buy books (except for the ones I read for the book clubs) and I have to juggle series depending on availability in the library (including ordering from inter-library loan.)