The Cow
The cow is just a cow. It will drop raw beef and leather which you can be made into armor.
The Pig
The Pig is your average, everyday derpy pig. But this pig is a rare breed of Herp-Derp Pig. The pig will drop Raw Pork Chop. They are also HIGHLY annoying.
The Sheep
The Sheep are the only animal that don't drop any food but they drop wool. They can be dyed any color in the game. Red, blue, green, yellow, you get it.
The Mooshroom
The Mooshroom is only exclusive to the Mushroom biome. If you use shears on them you will get mushrooms and it will split into two cows. if you use a bowl on them you get mushroom stew. Drop the same things as cows.
The Chicken
The Chicken is, well, a chicken. It lays eggs and when you kill it, it drops Raw Chicken and feathers. Also SlyFoxHound's favorite animal to hit with a shovel.