I have goldfish too! They're Comets and almost monsters. I had a Polypterus in with them for for a few weeks. In the beginning they got along really well...then I had to take the Poly out.
I have a few fish in with my gold fish that technically "dont belong". They are refugees from other tanks that have had problems and include an angel fish, two Iridescent Sharks and a pictus cat. They all get along fine.