Which command combos do you personally like to use? I think we all know about the likes of 2-swords and X-Fight, but how about something a bit more obscure?
I have always had a fondness for the Geomancer's Earth ability when used in conjunction with magic commands. This is because it's a decent magic attack, and it does not consume any MP to use. Admittedly some of the damage can be slightly random, but I suppose there has to be a trade off somewhere.