For me, that succulent is crassula barklyi. My own largest specimen is pictured here. After I neglected it for two months, it finally started doing pretty well. Look at all those babies sprouting out of the stack on the lower left-hand side.
I love the structure of crassula barklyi. If it's grown in perfect light (better than the light I can give it right now, alas), the stacks are almost perfectly smooth. I'll admit that it's not the easiest crassula to propagate, but it's certainly not the hardest (I'm looking at you, c. columnaris).
What's your own favorite "underrated" succulent? I'd love to publish a list of readers' underrated favorites! Either comment here or email me real quick and tell me the first one that comes to mind. Pictures welcome, too.