I have False Juliis (Leopard Cories) in my 55, a school of 6, and they are fun to watch. A few will swim in at the bottom of the bubble curtain, float to the top, swim out and down, and do it again for 5min or so. It's like a roller coaster for them. Also, at feeding time, I'll drop in an algae wafer and one will pick it up in its mouth and the rest will chase that one around the tank until he drops it. After it softens up and gets spread out a bit, you can see all of their tails sticking up in the air all in one spot as they're cleaning the gravel. They're really quite funny.
I also have some Peppered Cories in my 10 gallon with my
betta. They act pretty much the same, but on a smaller scale, and they seem to school more than my Juliis do, though they don't dogpile like the Juliis (or at least not yet). You really can't go wrong, just pick the style you like.