In its ever-growing mountain of content, Minecraft has just added rideable horses in version 1.6 on PC. Horses are bred using wheat and can be equipped with armor to keep them protected. They can climb up hills, and by holding down the space bar they can be made to jump farther. Chest-carrying donkeys have also been introduced.
A few other items have been added such as leashes for tying up animals and carpets. This new build of Minecraft was built on Java 6, so there are a lot of behind-the-scenes changes that you won't see. It requires OpenGL version 2.0, which will allow some better back-end stuff to happen in the game's engine.