There are 3 cats in my household currently and I can tell them all apart... but they are really quite different.
Tumbleweed is very quiet and rarely meows. When he does it's the sweetest, saddest meow (because he wants something).
Mallow sounds like he smokes 6 packs a day so he's easy to tell apart. The most vocal of all the cats and will start asking for dinner up to 3 hours early. It is non stop meowing until he's fed. Sometimes he goes to meow and squeak comes out.
Ozzie (my parents' cat) doesn't talk a lot, but when he does it's LOUD. Usually when he's prowling the house. You'll just hear a loud MEOW out of nowhere. He also screams when he's playing/fighting with the other cats and it sounds like bloody murder even though no one is touching anybody.
This house is very much a "mom he's breathing my air" house.