Personally i think goldfish should be kept with other goldfish only. but there are a few fish that can live with them. never ever get a common plec, they will get huge and attack your fish when they get older. Dojo/Weather loaches are good, they need quite a big tank for swimming room and grow to about 1ft long. you can keep a shoal of small fish like white cloud mountain minnows or danios but as the goldfish get big they are likely to eat the small fish.
bristlenose and rubberlip/nose plecs are good too.