I like a good history book, one that delves into technological, societal, etc. developments a group of people go through as opposed to, say, a book on a single famous historical figure - I despise biographies.
I also like detective/mystery stories, though it has to be the right kind. I'd say the same for scifi, which is a genre I rather like, but am extremely picky about. Scifi that's too hard (as in hard scifi) isn't usually my thing because it usually turns too much to wars and guns and empires and boring stuff like that when it could be about exploring and developing new ideas.
I also read a lot of fantasy, but again it's got to be the right kind. I don't normally care for sword-and-sorcery, high-fantasy unless it's something at least a few decades old. Something that's more Harry Potter in scope is more my thing. It's got a good helping of mythology, legend, and fairy tales and that's all good stuff to have. If the story slides a little into horror and/or dark fantasy that's not bad at all.