Different cory species may school as long as they have similar color markings. There are several species which look like the panda, keep an eye out for those. There is a risk for hybrids if they breed, though.
A cory may also school with completely different species, but that's because it's very lonely and it's not the best option as far as the fish itself is concerned. Still, better than keeping it all alone, I suppose.
I haven't kept glass catfish myself, but I've been told they're schoolers as well, maybe even more so than cories. Checker barbs, bala sharks and clown loaches should also be kept in groups. Oh, and clown loaches have been known to eat cories' eyes, it might be best to move the cory you have and get it more friends in another tank.
(As a word of warning, as the chinese algae eaters grow older, they will become increasingly intolerant towards each other and need a more meaty diet. They may also become aggressive towards other species.)
By the way, even if you don't add any more fish, your foot-long fish will still outgrow the 55 gal and in a way overstock it.