Some months ago I got sick of feeling guilted by having The Picture of Dorian Gray, Tender is the Night, and Pride and Prejudice staring at me from my shelves, so I read them in quick succession.
Now it is mainly history books by ancient authors I haven't gotten 'round to reading. I love such books but they are not exactly light reading and require a greater attention span than I seem to have nowadays, so they sit. Particularly troublesome is Tacitus, which I've had for ten freaking years. One day, I tell myself... one day. My husband sometimes picks up books he's had for even longer and finally reads them, so that gives me hope.
When I own the books, I feel like I can read them at any time, so I end up reading library books with a due date first.