I'm using a broad(ish) definition of 'Ancient World'. I was going to limit it to BC, but one chap absolutely demanded to be included (in the 1-5 piece which will follow this). In reverse order, here are the lower half of the top 10.
Number Ten: Leonidas
The King of Sparta is tremendously well-known, and his fame was only increased by the recent film 300. He's famous for just one thing, but as one things go this is pretty impressive. When Xerxes, Great King of Persia, was invading Greece with an enormous army the city states decided (for once) to co-operate. However, they needed time. Leonidas led 300 Spartans in the defence of a narrow pass called Thermopylae (Hot Gates). Previously the force had been larger and included some other soldiers, but once it became clear a traitor had shown Xerxes a secret path that would encircle the defensive position Leonidas ordered the non-Spartans to leave. For days he kept at bay a force that outnumbered his by hundreds, perhaps thousands, to one. When defeat became inevitable he met it as resolutely as Constantine Dragases would almost two thousand years later. And, ironically, the king of an oligarchic state saved democracy in Athens.
Number Nine: Brasidas
Not a household name, but perhaps the most able general in the Peloponnesian War. Brasidas showed strategic cunning, a slyness of wit and personal bravery when he (briefly) spearheaded the Spartan war effort. However, his fortune did not match his valour and he was one of a handful of casualties sustained in combat with the Athenian forces.
Number Eight: Julius Caesar
Some say he's better than Hannibal Barca, but he isn't. Caesar was very strong logistically and strategically, and engendered deep personal affection amongst his soldiers. He was responsible for making Gaul submit to the eagles and won the Civil War against his old friend Pompey, reshaping the history of Rome and the world.
Whilst not the first emperor (that was Augustus, his nephew) he did decisively shift the destiny of Rome away from a decrepit republicanism towards an imperial path. He also changed the calendar (lots of chaps tried this but only July and August have stuck) and his surname came to mean 'king' in umpteen languages.
He also invented the comb-over (according to QI).
Number Seven: Hamilcar
The father of Hannibal Barca (his sons were referred to by some as the lion's brood), Hamilcar was actually pretty fantastic in his own right, not unlike Philip II and Alexander. During the latter stages of the First Punic War he was in charge of Sicily and, using the tactical brilliance that would prove hereditary, gave the Romans quite a seeing to. Unfortunately the war was really a naval one and through no fault of his Carthage surrendered.
After this the city state couldn't pay the wages of its mercenaries, which was a dangerous situation. Hamilcar gathered what troops he could and chased the mercenaries away, then dogged their footsteps and annoyed them so much that they began to chase him. He led them into a narrow canyon, blocked the exit and cut them to pieces.
That wasn't the end of his victories though. He went to Iberia and began conquering the land, which included lots of lovely silver mines. He was killed in action there, and replaced first by Hasdrubal the Handsome, his son-in-law, and then Hannibal.
Number Six: Marius
Marius was the uncle of Julius Caesar and a big figure in history for reasons beyond that. Through cunning he managed to wrest control of the Jugurthine War, which he subsequently won, from his former patron Metellus Numidicus. After this he achieved the not inconsiderable feat of defeating the Cimbri, a tribe that had slaughtered Roman armies thrice before (including at the disastrous Battle of Arausio).
Marius also engaged in military reforms, and although the precise nature of some of them is lost in the fog of history their legacy was known by the name of Marius' mules given to soldiers (because he reduced the number of baggage animals so the men had to carry almost everything themselves). His political ambitions meant that he weakened an already creaking political structure, and perhaps provided a template for his nephew to follow.