The company I am currently working with on a project (Zzyzx Polymers) has the capabilities of mixing virtually any additive into plastic in the effort of eventually extruding it into a usable filament. Some materials we currently are working with include, but are not limited to:

1. ABS/Coffee grounds
2. ABS/Ocean plastic
3. ABS/Chicken feather
4. ABS/Tire rubber

The above additives can also be mixed with PLA. If anyone has any specific products they are looking for or specific additives that they would be interested in, please feel free to comment with suggestions or requests.