For a while I kept one in with a goldfish, 2 cories, and a pleco - in a 10 gallon - with minimal water changes. Needless to say that tank failed and I got smarter since, but for the time the frog did actually get along. Note that I do not recommend this mix though. The frog never got big - it was likely stunted.
Clawed frogs are quite the voracious predator when cared for well. Try going for males - they are smaller and therefore there is a wider tankmate range. Realistically, any fish you put with it should be considered a feeder. Small fish will eventually get devoured - guppies/other livebearers could probably last for a bit depending on cover and gallonage. Anything too big for the frog to eat is liable to attack the frog.