Sleeper goby and other related species are the best sandsifters, but they will pretty much kill off any invert in the sand. If the sand is live, the worms and critters in it will pretty much take care of themselves without any specific sandsifters, but if you insist, you can look into sea cucumbers and others.
dont get a sand sifting starfish, they allways die, even in huge systems. I think queen conches are best, and nassarus snails, not only do they sift but they also stirr a little too.
I've had my sand sifting stars for nearly 3 years (almost as old as the tank setup). They're doing a great job in there. They've never disturbed my herd of feather dusters either.
