Mobs: Peaceful and Hostile

First, I'll start with the peaceful mobs.  These mobs are friendly.  Some flee for a few seconds after being attacked by a player.

• Sheep this mob is very easy to find.  Sheep drop wool when you kill them, but to avoid killing sheep, you can use shears (crafted with three iron ingots).  
• Pigs this mob is also very commonly found.  When you kill a pig it may drop 0-3 pieces of raw pork chops.
• Chickens when this animal falls off of a cliff, it can slowly flutter down with the help of its wings.  Chickens drop either a feather or raw chicken when you kill them.  They can also lay eggs in random places occasionally.
• Cows when this mob is killed it drops raw beef or leather.
• Mooshroom this mob is like a cow, except it is red with white spots, has mushrooms on its back and head, and its eyes are black.
• Squid this mob just calmly swims around in water.
• Villager a villager is found in a village with lots of others usually.  They can trade with you, and they can also open doors.  Tip: they really like emeralds!
• Bat this mob is obviously found in caves.  They are speedy and zip around the underground in nothing flat!
• Horse you can find some horses in a group while traveling your world.  To tame it, you can keep right-clicking it until hearts show up.  You then can use your saddle to control it.
• Ocelot ocelots are found in the jungle and they are very fast.  They look very similar to cats.
• Cat (domesticated ocelot) you can make ocelots a pet cat!  Just go fishing and feed them fish until they turn into a cat.
• Rabbit this mob is new in the 1.8 update.  These may be tamed with carrots.  Just like ocelots, they are sensitive around players.  Unlike dogs or cats, they cannot be able to sit down.  Drops include rabbit hide and rabbit's foot.

Dog (domesticated wolf) to make a wolf your pet, feed it some bones from skeletons you have killed.  They will stay by your side and attack foes who may cross your path!

Hostile Mobs:

These mobs attack on sight

• Blaze spawns in the nether.  Can fly and uses fire as a weapon.  Will throw fire at you until you die.  Blazes drop blaze rods.
• Cave Spider smaller than a regular spider and re-textured to a dark blue.  Slightly more dangerous, can fit through 1x1 holes, and can climb walls.  Sometimes in combat they will poison you, turning your health bar green-yellow which will gradually wear down to half a heart.  You can stop the poison by drinking milk.  These only spawn in caves.
• Creeper this mob is widely known in the minecraft world.  It looks tall and green with a frown-like face.  When you hear a sssss.... sound, quickly back away!  If you get too close to a creeper it will blow up, causing damage to your health and your land.  If you kill a creeper, it may drop gunpowder.
• Ghast this spawns only in the nether.  It's appearance is a large white mob with a sad face/ tears coming down.  It will throw fireballs at you.  Don't forget that it has a large attack range and can hit you.
• Magma Cube this mob is particularly interesting to me.  It spawns in the wither, and is known as a nether version of a slime.  Magma Cubes slowly jump in different directions until a player is in range.  They are unique because they do not drown in lava.  Water itself doesn't hurt one, but it can drown in water.  Magma cubes don't take fall damage, and whatever the size, it can jump 3 blocks tall!  When Magma Cubes jump they spread out into 8 layers.  They drop magma cream when killed, which is used in potions.
• Silverfish this mob is found in strongholds either from monster spawners or from monster egg blocks.  Monster egg blocks noticeably mine a little slower than regular blocks.  Monster egg blocks are regular stone, cobblestone, and stone bricks.  They can be very aggravating because when you mine a monster egg block, it may awaken monster egg blocks nearby. This will create a terrifying storm.  
• Skeleton this is spawned very often and easy to find almost anywhere.  This mob uses a bow and arrow and can shoot from a distance.  Never try to attack it up close, as it can keep knocking you back with arrows until you die.  I suggest using its own weapon against it, and staying from a distance, making sure it does not see you.  When the time seems right, shoot a skeleton until it dies.  Mob drops can be bones, a bow and arrow (sometimes), and maybe armor if it wore any by picking it up.
• Slime this is a rare hostile mob found in swamps or underground caves.  They will commonly spawn in the world type Superflat.  They have four different sizes, large, medium,  small, and tiny.  Tiny slimes are harmless to the player.  When killed, a big slime will split into two medium sizes, and then to multiple tiny slimes.  Only tiny slimes drop 0-2 slime balls, which can be crafted into sticky pistons.  They cannot swim (which means they can drown) or jump in water.
• Spider these are hostile at night and neutral during the day.  Do not let them get on higher ground than you, because they will pounce on you, causing a lot of health loss.
• Spider Jockey this is one of the rarest mobs in Minecraft.  The appearance comes as a skeleton riding on a spider's back.  This is deadly because skeletons can shoot arrows at a range and spiders can pounce at you.