Mob Types

Type ID	Type Name	Metadata
50	Creeper	Index 16 - byte - possible values: -1, 1. Referred to as "max damage" in MCP.
51	Skeleton
52	Spider
53	Giant Zombie
54	Zombie
55	Slime (random size?)
56	Ghast
57	Zombie Pigman
90	Pig	Index 16 - byte - set to 1 if the pig has a saddle, 0 otherwise.
91	Sheep	Index 16 - byte - Bit 0x10 indicates shearedness, the lower 4 bits indicate wool color.
92	Cow
93	Hen
94	Squid
95	Wolf	Index 16 - byte - Bitflags (see below) Index 17 - string - Name of the player who tamed the wolf Index 18 - int - Health of the wolf
120	Villager (1.9 pre1)

Sheep Wool Colors

Index	Wool Color
0	White
1	Orange
2	Magenta
3	LightBlue
4	Yellow
5	Lime
6	Pink
7	Gray
8	Silver
9	Cyan
10	Purple
11	Blue
12	Brown
13	Green
14	Red
15	Black

Player, Index 0

Metadata index 0 is a byte representing a set of 8 boolean flags:

Bit index	Bit mask	Meaning
0	0x01	Entity on fire
1	0x02	Entity crouched
2	0x04	Entity riding
3	0x08	Sprinting

Potions, index 8

Metadata index 8 is an int representing potion effects:

Value	Meaning
0	No potion in effect

   0x5A6C81 Slow
   0x7CAFC6 Speed
   0x7CAFC6 Speed II
   0x7098AF Speed II + Slow
   0x6B8DA3 Slow + Speed

Wolves, index 16

Metadata index 16 for wolves:

Bit index	Bit mask	Meaning
0	0x01	Sitting down
1	0x02	Agressive (red eyes)
2	0x04	Tamed

Creepers, index 17

Metadata index 17 for creepers (This may apply to other mobs):

Value	Effect
0	normal
1	creeper that got hit by a lightning gains a blue aura. http://www.youtube.com/watch?v=uq0Lm1EULxQ
2, 3, 4 and 255	no apparent effect
other values	unknown, not tested