ATI (the Hydro-Sponge company) have a Filter-Max pre-filter that seems to work quite well and is better at resisting clogging than the make-shift sponge pre-filters that people seem to use most of the time.
I think they have more than one size. It is vastly better than any other pre-filter sponge. It is a heavy duty material that lasts a LONG time and has a nice snug fit. Most others have a flimsy sponge that breaks apart in a few months or falls off.