I found another two of the "trilineatus-type" corys at another pet store today. That gives me a total of six of them - hopefully it will get me some good schooling behaviour. I was looking for characins again, but once again nothing jumped out at me. Nothing but corys, that is. The two I bought were in a tank of "spotted Corydoras"; I have two of the other species, but I didn't want to buy too many fish today. I was also tempted to get some more Corydoras aeneus and maybe to finally buy some C. paleatus, but I managed to resist the temptation.
I actually went to the pet store in search of some Otocinclus - the February issue of Tropical Fish Hobbyist has a good article on them by Gary A. MacDonald of TropicalResources.net. MacDonald says that not only are Otocinclus very social fish (and recommends that they never be kept in groups of less than three), but when the groups exceed 12 individuals interesting dominance hierarchies emerge. Having read that, I felt the need to expand my collection - after all, I only have two in my main tank. Unfortunately, the pet store only had two left. Since I have no way of being sure which species of Otocinclus I have, I would rather purchase a bigger group - that way I'm more likely to get several of the same species.