You'll be fine for a while as long as they're small, but eventually... as everyone else said. You get the picture.
Anyway, as far as compatibility, I have had my goldfish with bettas, BS tetras, mollies, and they get along fine. However, the risk you run there is the temperature compatibility. I keep my goldfish at a rather warm 72/73, which is comfortable for the tropicals too, but I'm also working on finding new homes for my tropicals so I can drop the temp for the goldfish into the high 60s.
I hear that white cloud minnows do well at cool temps, so you might want to look into them? As far as getting along though, anything that doesn't nip fins will get along. Goldfish are very peaceful fellows. So if you can find some coolwater community fish, that would be a good idea.
I'd actually recommend apple snails, though. They do well at a wide range of temps, and they're just as personable and interesting as fish. Mine bubble-surf. They scooch to the top of the tank wall next to the bubbles, then literally jump off and surf the bubbles down to the floor. They do this over and over. They're really cool, and they can eat pretty much the same diet as your goldfish- dark greens and pellets.
