What kinds of fish are ok to put with african dwarf frogs?

Maybe a betta or another african dwarf frog.

Don't do the betta- bettas dont get along well with other aquatics. Honestly, I would get a bigger tank before you add anything. Maybe a 15 or 20 gallon? Then add 1 or 2 more african dwarf frogs, (not african clawed, they will shred everybody else to pieces XD!) 2 albino cories, and 3 goldfish. That's what I have had and they all get along fine A pleco would be nice too. I also have 3 red minor tetra, but I don't recommend putting them in with goldfish. Surprisingly mine get along but they aren't really meant to be put together. Here's a piccy of my old albino cory and froggy http://www.flickr.com/photos/boomerproductions/2127479239/in/set-72157603556189273/

I would say the 1/2 gallon tank would do best with only the frog.