I usually teach my villagers phrases that apply to their personality and look. For Rudy it's "Mmm Fish", For Sterling it's "Yo wassup", for Midge it's "Twello". Yup... pretty un-creative XD. Welp, that's how it is.
I've made a few say Moshi Moshi as a greeting but Julian says Hold your horses! And Clyde says Haaaaay.
Marina has a catchphrase of Bloop
The horses say sugar cube
I made Stitches catchphrase be honey because I thought it was adorable for him at the time. Unfortunately now Wolfgang uses it as well...and it just doesn't seem all that cute now.
Drake's greeting is Flying Fishes! I still don't know what possessed me to have that.
I try for something to be unique to the characters, species and personality wise but it can be hard.
I recently gave Rudy the greeting, "I've got the Chalk!"
It's been a good while since I got a request. It's mostly them trying to give me some stupid new nickname.
I have all of the hamster villagers and they're like my moogles, so I've been changing their catchphrases to "kupo", Twiggy's to "keen", and my various bunny villagers are "err err" (because Bun Bun would kinda grunt and it sounded like that, lol), except for O'Hare. He says "o'bun".
For their greetings I have them address me formally, generally "Your Majesty" or "Your Highness". For Dotty though I have her say "Your Bunnies" because she's just so cute and peppy ^_^ For their catchphrase, its generally also "Majesty" or "Highness", just so I'm sure they remember who the ruler is around town ^_~