Customizer TanoTrooper has a series of historically themed minifigures called TTfigs that utilize minifig and brick-built elements for a truly unique and custom look. But that's not what caught Ochre Jelly's eye...
Take a look at the TThorse, a brick-built beauty with all the right levels of articulation. Yes, it kinda gives your steed a 'robot-horse from the the future' look, but the posing one can accomplish with this is worth it.
TanoTrooper's Flickr stream. Oh, and if you can get over his inherent dislike of the fig, I recommend The Living Brick for some outstanding 'organic' MOC coverage.
UPDATE: You can find instructions for the TThorse via Eurobricks.