Actually, some plecos get quite large, so I agree with the no pleco thing. I personally have spotted cory cats (feel free to view my gallery) and they are great. Keep in mind though, they will eat food that falls to the bottom, but you need to also supply sinking shrimp pellets to be sure they are getting their daily nutrients, etc.
If you are strictly looking for a scavanger however, look into the rubber eels. I have found them at my lfs
and am seriously considering buying one for the next tank I set up. They are blind and are shy (which is why they scavange the floor of the tank) so you need to make sure if you go with this guy that you provide good hiding places for them.