We have recently added the plugin PetCreeper, which adds the ability to tame, ride and teleport any vanilla mob. So far, I have configured it more or less the way I want it to be. The only issue so far is, I cant get it to work with horses. They might not have finished adding the ability to tame them with the plugin, but the plugin works so well in every other regard, so I saw no reason not to leave it in, for now at least.
I have set it up to allow the following:
You can tame a cow with seeds, tame a chicken with rice, tame a sheep with sugar cane, tame a pig with feathers, tame a wolf with raw pork, tame a ozelot with raw fish, tame an irongolem (built yourself or found in a village) with an iron ingot, and tame a mooshroom with a red mushroom. You can also ride cows, mooshrooms and pigs. Just punch the air in the direction you want it to go.
Plays can use the following commands:
Also, you can right click your pet to toggle whether or not it follows you. I have learned from experience that if you have fly on, you do not want your pet following you. It will teleport to you, and then drop to the ground and die. Additional mobs may be enabled for taming/riding in the future.