There is a decent tutorial to do muscle ups on beastskills. I have been working on my pull on a bar, with the goal of getting a muscle up(or multiples, eventually) on both a bar and rings. Can't be too hard if thousands of crossfitters can do them...
Also bought this guy recently, to work on ring muscle ups and iron cross(another goal):
Tried it out today, can't even get to parallel on the farthest setting(straps out near elbows, shortens lever arm and makes it easier). So this is going to take a while, but I figure I need some goals. I can do pullups with half my bodyweight, but can't do those. Figure it will help toward a one arm chin/pullup as well.
Decent birthday, I must say. Fatgripz, my first CoC gripper(the Trainer, I suck), a chest rig for work, and now the ring trainer.