I did not plan it, but it seems that I'm on the way. I got all the baseball ones, and most of the Moon ones. I would not have gotten them if they were ugly, but baseball and the quest for the Moon have been two of the things that interested me the most since childhood, so those were coins that I actually bought because of interest in the subject. I'm not much of a commemorative collector otherwise, although I thought the gold Liberty from a few years back was a very elegant coin. But back to your question, it would be interesting to try to think of coins that could be convex without it being a gimmick. I think I saw something about a basketball coin, which makes sense. Maybe the NASA theme could continue with a tribute to some of the flights to the planets, but the rings of Saturn could be a problem. But a coin with the surface of Mars on the convex side and the rover on the concave would be cool, likewise Jupiter on one side and Voyager on the other.