Heartless
Shadow
The most common heartless. It is pretty easy to beat.
Soldier
Can attack with a few different moves. Parry it's attacks and use Cyclone to finish off it and surrounding enemies.
Nightwalker
It is resistant to beginning magic. It is easily defeated even with the Kingdom Key.
Rapid Thruster
One of the most common enemy in the game. In large groups, use Aero Trap to defeat multiple Heartless at once. In small groups, just jump and attack.
Bolt Tower
Assault Rider
Large Body
Lance Soldier
Hook Bat
Gargoyle Warrior
Gargoyle knight
Creeper Plants
Rabid Dog
Trick Ghost
Minute Bomb
Aeroplane
Hammer Frame
Hot Rod
Air Pirate
Cannon Gun
Undead Pirate
Fat Bandit
Fiery Globe
Fortune Teller
Icy Cube
Luna Bandit
Silver Rock
Driller Mole
Emerald Blues
Toy Soilder
Wight Knight
Living Bone
Shamen
Aerial Knocker
Silver Rock
Book Master
Morning Star
Surveillance Robot
Devastator
Emerald Blues
Magnum Loader
Srafer
Crimson Jazz
Armored Knight
Morning Star
Neoshadow
Bulky Vendor
The rarest Heartless. It is found anywhere breakable objects (suits of armor, fireworks stands,etc). Wait as long as possible to use the Reaction Command.
Crescendo
Tornado Step
Graveyard
Nobodys
Dusk
Creeper
Assassin
Samurai
Dancer
The Dancer is a Nobody that appears mostly in Hollow Bastion. It is controlled by Demyx.
The Dancer has a very effective fighting style. It will kick Sora vigorously for an extended period of times. Each kick sends Sora a few feet into the air. The most deadly attack comes when the dancer is sliding with glowing hands; if one touches Sora while doing this, the dancer grabs Sora and jerks him around in a dance before kicking him for high damage. (This is the "low posture" the journal mentions below.) They are difficult to defeat in large numbers.
They are one of two enemies that are feminine in appearence, albeit a sexy one, the other is fortuneteller.