What book do you keep meaning to finish but never do?

I've been a librarian for going on fifteen years, and the number of patrons who sheepishly confess to lugging around the same half-read book for months is startling. I have my own — a dense history of the Crimean War that's been marking my place with a receipt since March. It's not that it's bad; it's that I know exactly how it ends, and somehow that's enough for now. What's yours, and do you ever actually get back to it?