Wow, that's a tough one! I'll try to narrow it down.
Lily - When she gets into spaz mode playing with her toy. And when she nuzzles up into my neck for cuddles.
Chester - When he gently and politely wakes me up in the morning. He jumps up on me and stares at me, then, if I don't wake up he'll just settle down for cuddles until I get up. And also when he reaches for me if he's not done getting pet.
Bynx - When he brings me his wand toy wanting to play. The look on his face is priceless. Also, he's always the first one to greet me at the door.
Isabelle- when she comes to purr, snuggle, and head butt me when I'm feeling sad and crying
Persia- when she trills while playing with toys
Katrina- how she loves nose bumps, whenever she is on the cat tree and I'm walking by, I stick my face in hers and she bumps her nose on my nose