Not an expert on history, so forgive me if these choices are subpar:
1. Battle of Gaugamela, 331 B.C. - Cemented Alexander the Great's control over Persia, and initiated the Hellenistic period.
2. Battle of the Milvian Bridge, 312 A.D. - Ended a period of strife in Rome, consolidated power to the emperor, and legalized Christianity. If Constantine had lost here, Christianity would've passed away as another obscure cult.
3. Battle of Yarmouk, 636 A.D. - Saved Islam from domination by Byzantium.
4. Battle of Ain Jalut, 1260 - Curbed Mongolian influence. This is the Eastern version of Tours, but it's far more significant.
5. Battle of Leipzig, 1813 - Finished off the empire; though the Hundred Days were quite dramatic, the end of the Napoleonic Wars really happened right here.