David B covered the PetEmote addon way back in the beginning of this year, and now the Great Green Hunter has posted some really great ideas for custom pet emotes, for a few different families of Hunter pets. PetEmote lets your pet automatically show up in your emote text randomly, and is really good for giving your pets a little more personality of their own -- instead of just doing what you say all the time (and eating all of the food you've got to buy), PetEmote can make it seem like your pets are doing their own thing: chasing a stray bug that passes by, flicking their tails, or "giving you a sly look."
GGH's descriptions are really great, but of course whatever goes in the "Localization LUA file" in the PetEmote addon folder is what shows up in the game, so you can customize it as necessary. If you want to say your cat "waggles his butt, ready to pounce," you can do it.
Of course, if you think of your pet as just a DoT you have to feed, you might not be so interested. But having a pet and keeping track of where it is is such a huge part of the Hunter class (though PetEmote works for Warlocks as well) that giving your pets a little more personality goes a long way in game.