Although it's not a novel, I can't imagine how any list would ignore Heinlein's "By His Bootstraps" which posits the future as being as unchangeable as the past. Another great book with time travel is A.E. Van Vogt's "The Weapon Shops of Isher" where a time traveler is bounced from past to future, collecting more time energy along the way, which will have to be released sometime with explosive results. And that's just a subplot!