What if Jesus were never crucified? He could have been killed a number of other ways. Poisoned? Stabbed? Fed to lions? Maybe he just died of natural causes. What changes would we see, both in Christianity and history as a whole?
Obviously, crosses would no longer symbolize Christians, which would change heraldry forever. Also, I'm guessing that crucifixion is going to remain a popular method of execution in Europe even after Christianity takes over (assuming it does). Anything else?