Just to balance the US domination of this thread. I have never been able to stand Patton, and less so beacause my last Adjutant thought him the best thing since sliced bread.
My favorite commander from way back is an obscure guy called Gen Sir Garnet Wolsely from the 18th Centuray. Led a group known as the Wolsely Ring who lobied for the professionalisation of the BritishArmy, and who was perhaps the first proponant of manouvre warfare, as shown in Canada.
However, most successful commander has to have been, with no shadow of a doubt, a guy called Field Marshall the Viscount Lord Slim, who commanded Allied troops in Burma in World War Two. He not only managed to blend together an Army of more nations than had ever been assembled before, but managed to take that Army from defeat through further defeat, then rebuild them to beat an enemy previously thought to be invincible, and push them out of the most terrible terrain fought through in WW2.
I recommend the books, 'Defeat into Victory' by Slim himself, and perhaps above all oiver military books, 'Quartered Safe Out Here' by George MacDonald Fraser. A rare Gem of a book.