It's fairly normal for me to go through periods of buying the same kind of plant, or sometimes even multiple copies of the exact same plant, and then realize that I was doing this only somewhat later. Most of my orchids all arrived at about the same time, for example, as did most of my African violets (which also all left at about the same time, too: African violets are social plants, and travel in swarms).
Lately I seem to be having a cactus period: in addition to the Astrophytum ornatum I mentioned a while ago, I've also gotten a couple other cacti recently, plus an Agave which, though not a cactus, shares enough characteristics with cacti that I think we can include it as an honorary cactus for these purposes.
UPDATE: I now believe this is probably not a Myrtillocactus after all, but a Stenocereus pruinosus. This is based on their respective photos at cactiguide.com.
UPDATE: I now believe this is an Isolatocereus dumortieri. Which I am okay with.