I've avoided this thread for far too long as it's really hard for me to pick just a couple... and it seems like they've all been said already!
Hmmm, lemme think... always thought Murat was pretty interesting guy, although admittedly not the most skilled of the Marshals, and a bit of a scumbag.
Also, no mention of Philip II of Macedon or Pyrrhus of Epirus? They were certainly effective commanders, albeit overshadowed by their son and (second) cousin respectively.
Nice to see Tsubodai getting some rep here, he's often overlooked. Genghis hardly did it all on his own (although the whole unification of the tribes was his doing).
Baibars: commander of the Mamluks, helped crush the Seventh Crusade, decisively defeated the mongols at Ain Jalut, and (likely) took part in the assassination of the previous sultan of Egypt before taking the throne himself. The first Mamluk sultan then went on to seriously mess up what was left of the crusader states. He was also an effective administrator and highly popular in the Muslim World.
Belisarius: the Byzantine general responsible for the Byzantine reconquest of much of the western Mediterranean under Justinian (despite a marked lack of support from the Emperor). Notably defeating the Vandal Kingdom in North Africa and the Ostrogothic Kingdom in Italy. Belisarius' conquests in orange below: