I would say most kinds of tetras would be ok. I might steer clear of serpae tetras though. People say if you have at least 6 or more of them together in a tank that their aggression will be limited to one another, but I've had some very iffy individuals that still targeted my cories and such. Oh! Cories would be a good mix, that is unless you want to breed the galaxies. I hear they scatter their eggs and I'm sure cory cats would not be above sucking up the eggs. Small livebearers like guppies and even platies would be fine, I'm sure. I will be sticking my galaxies with my heterandria formosa livebearers and a pair of honey gouramis. It's hard to say which family of fish galaxies would go well with, because just like most every human's family, there's a black sheep in the midst
. Fishgeeks.com and fishbase.org are good places to get reliable info on husbandry needs of fish. You can look up fish you're interested in by typing in their common names when using the aforementioned websites, but it's easier to find fish if you know their scientific names. Try and find fish that are considered peaceful, that's the main thing. I would say steer clear of fish that are nearing the 4" adult size range, but then I think of the pearl gourami that is said to sometimes get to 5", and it is a very good community tank resident. It has a pretty small mouth too, which means it wouldn't consume adult galaxies (though eggs and fry might be fair game). Galaxies don't seem to be demanding as far as water parameters or feeding is concerned. Just be mindful of their tankmates. I hope all this rambling I've done has helped a little!