Go for sand sifting stars (some don;t like them cause they believe it to go after the goodies in the sandbed (which they do) but I suppose it depends on how deep or how much of a sandbed you have....
I used to not want hermit crabs, but they are seriously great to have for cleanup (scarlet & blue legged), and of course snails...shrimp (peppermint & Skunk) are great little cleaners too, but I think the small hermits do the best job. I do like the sand sifting stars (i have a 6" sandbed) cause they keep the top surface moving without disrupting the depper layers)