Generally, goldfish should only be kept with other goldfish and sometimes koi if they are kept outside in a large pond. Mixing goldfish with other fish species is often not a good idea , because of disease transmission and other factors.  Goldfish also should not be kept with tropical fish species due to different temperature requirements.

Goldfish should usually be kept only with their own kind, because of (earlier mentioned) the risk of disease transferred from the tropicals/catfish that may not harm them but could be lethal for your goldfish. And for the reason that they usually have different preferences for temperature, hardness and alkalinity of the water from goldfish.

But my mother has been keeping her goldfish with black mollies, platies and corydoras for instance without any problems. So I'd say that if you feel like you need to have a catfish cleaning for you, then some peaceful species of corydoras might be in order. Possibly some Loricariids (Suckermouth catfish) if you have trouble with algae growth (:
I only have positive experiences with these species myself, but still, be careful with what you mix with goldfish.
Besides, goldfish enjoy digging in the gravel to find edible items too, so they should be enough to keep their home clean (: