Some of Cassie's meow meanings:

Hi, I'm glad you're home. It's about time you showed up, what took you so long?
Human, where are you?
Put me down NOW or I will be forced to dig in with my claws.
Wake up!
Feed me!
I am in the spot where I go to receive a treat and you didn't give me one -- what's up with that?

She also has a little sound kind of like "muurrrp" that she makes when she is content. Sometimes she will go like "mmrrRRRrr" when she is looking out the window at birds or bugs.

And one - meEEEOOOOW! that usually means I've stepped on her tail. She has this funny way of placing herself between my feet, without making a sound, when I'm standing at the bathroom sink or the kitchen counter. Over the years I have learned to look down before I move!