List of valid entity types for minecraft server version 1.8.8.

ARMOR_STAND
ARROW

An arrow projectile; may get stuck in the ground.
BAT
BLAZE
BOAT

A placed boat.
CAVE_SPIDER
CHICKEN
COMPLEX_PART
COW
CREEPER
DROPPED_ITEM

An item resting on the ground.
EGG

A flying chicken egg.
ENDER_CRYSTAL
ENDER_DRAGON
ENDER_PEARL

A flying ender pearl.
ENDER_SIGNAL

An ender eye signal.
ENDERMAN
ENDERMITE
EXPERIENCE_ORB

An experience orb.
FALLING_BLOCK

A block that is going to or is about to fall.
FIREBALL

A flying large fireball, as thrown by a Ghast for example.
FIREWORK
FISHING_HOOK

A fishing line and bobber.
GHAST
GIANT
GUARDIAN
HORSE
IRON_GOLEM
ITEM_FRAME

An item frame on a wall.
LEASH_HITCH

A leash attached to a fencepost.
LIGHTNING

A bolt of lightning.
MAGMA_CUBE
MINECART
MINECART_CHEST
MINECART_COMMAND
MINECART_FURNACE
MINECART_HOPPER
MINECART_MOB_SPAWNER
MINECART_TNT
MUSHROOM_COW
OCELOT
PAINTING

A painting on a wall.
PIG
PIG_ZOMBIE
PLAYER
PRIMED_TNT

Primed TNT that is about to explode.
RABBIT
SHEEP
SILVERFISH
SKELETON
SLIME
SMALL_FIREBALL

A flying small fireball, such as thrown by a Blaze or player.
SNOWBALL

A flying snowball.
SNOWMAN
SPIDER
SPLASH_POTION

A flying splash potion.
SQUID
THROWN_EXP_BOTTLE

A flying experience bottle.
UNKNOWN

An unknown entity without an Entity Class
VILLAGER
WEATHER
WITCH
WITHER
WITHER_SKULL

A flying wither skull projectile.
WOLF
ZOMBIE