scrubbies, sponges, bioballs, pumice, lava rock, etc are all ok... but they aren't the most efficient out there.
If you have lots of $$$ to drop, sintered glass all the way. It has an absurdly high surface area ratio. Another option is a fluidized bed filter with sand. It's kinda of a PITA to make one, and buy them can be pricey... but there's no better bio filtration for large projects IMO. The sand is all kept in a state of suspension so every grain has a chance to be fully colonized.