This is the continuation of SpawnMob for Bukkit that was originally made/developed by Deven Lahoti (xmlns).
Version 4 and later barely uses any code from the original plugin.

Changelog
Version 5.0_BETA
BETA RELEASE (At least it works.)
This update breaks a lot of features, which of many I do not know that are broken. (This is why it is a Beta, at least it works.)
New Features:
Spawning of all new BASE (Guardians, Rabbits, Endermites) mobs works

Known Bugs:
The new craftbukkit release has broken the way I found if players are online, things broken due to this will be marked with a *
*Spawning mobs riding players or players riding mobs OR players riding players is broken.*
*Spawning mobs onto a player location is broken.*
*Anything to do with spawning things to on or with players is broken.*
Elder Guardian cannot be spawned.
Zombie Villager cannot be spawned.
Some other non "base" mobs can not be spawned manually LIKE:
** Colored horses and sheep
** Colored ocelots
** Baby zombies
** Any mob with armor or weapons

Developer Update
I will be completely re-designing this plugin with the knowledge I have collected in my first two years of college (computer science major).
When that finally happens, you can expect normal updates to this plugin and additional features to be added.

Version 4.1
Bug Fixes:
Plugin actually works now. Awesome.
Fixed the PermissionsEx bug.
Fixed misc. bugs.
Typing in commands from console no longer produces an error, try it.
Entering a command in a command block will no longer produce an error, try it too.

New (Known) Bugs:
Some horse spawning commands do not work. Will be fixed later.
Mob spawner can't be changed to mobs that have '_' in the name. Example: Magma_Cube
Other misc. bugs that I haven't found, please tell me of them.

New Features:
Added /sm reload - Used to reload the config files.
Edited the help menus to look better and explain things better.
Added code for later use. This is for you people who like to look at my code. ;)

Version 4 (Clean Slate)
COMMANDS ARE CHANGED IN THIS VERSION!
New Features:
A broken plugin. Don't use. Please just don't use. 
Go straight to 4.1, if your server isn't running MC 1.7.2+ then I guess you'll have to wait.
Horses
Spawn on player works fully again
Mobs riding things works again
Spawning on coordinates
Better command structure

Bug Fixes:
Fixed spawn on player and spawn riding bugs
Fixed ocelot killing bugs
Fixed ocelot spawning bugs
Fixed a heck ton of bugs (and even broke the plugin! I fail so hard.)