For real. Off the top of my head there's, MeerrrOOOOOwww MerrrOOOOwww, the loudest one, huge inflection in the middle. Generally while strolling through the house, back and forth. I think that's the "I'm bored" one. But he'll also do it if I stay up. If someone is out of bed past curfew he'll do it. I have to close the bedroom door or he'll wake the wife.
If you say summon him he'll probably ignore you but if he's interested he'll whimper errrderrruuderr softly while walking toward you.
Then there's, MOWLLLLL MOWLLLLL, slowly howling, that sometimes means he's sick and gunna throw up. Usually right on both the rug and the carpet.
Then there's, MAHHH MAHHH, just two in quick succession, which literally sounds like mama. That's the I want something one, generally he wants catnip from the outside plant.
Just heard him go MOOOOW MUUUROWLLL MUUUROWLLL howling, but he's just pacing back and forth from the window and now wimpering at me. So I assume he's misses mama (the wife).
The funniest is and most unique is, BRRRRAHDAHDOP, which he yells before tearing full speed through the house or down the hallway for seemingly no reason. I think that's either "Look at me" or he's so excited he can't contain himself and it slips out naturally.
Side note: this was an interesting challenge creating and optimizing these onomatopoeias