From comparing a few different reviews and my playthrough as well as my friends, I can say that aside from a few different scenes along the last chapter and its end, the game plays out mostly the same. The following is what I know:
When visiting the shelter (end of ch. 4), anyone in the group can stay or not (Omid & Chirsta either both come or both stay), if Ben is with the group he can come along as well depending if you get there alone; If you're not alone in the shelter, you have the option of cutting off your arm or not. Your infection will spread either way; Coming back home the boat will be gone. If anyone stayed behind he'll be locked inside the shed; On the way to the sign/bridge, if you have Ben with you, he'll fall off a broken balcony and be impaled. Kenny will be "overrun" protecting him (not implied if dead or not). If Ben isn't with you, Christa will fall down a skylight and Kenny will help her out, but he'll be overrun afterwards (again, not implied if dead or not); The bridge breaks when Lee crosses it whether Omid & Christa crossed before or not. You'll be separated either case. Omid & Christa won't return (unless you assume they are the shadowed figures in the post-credits scene); If you kept a weapon while talking with the stranger, you can attack him yourself, otherwise Clem will attack him. You may kill him or spare his life; Lee will collapse after Clem sees her parents. Near the security guy Lee can tell Clem to kill him or just leave him chained. If kept alive, Lee will turn. Clementine leaves either way; The end credits scene doesn't seem affected by any choice in the episode.