I have a 5-6 inch DSB in my tank so cleaning my sandbed was a primary concern for me.
I have about 15 nassarius snails which eat leftover/excess food that lands on my sandbed; they also help turn the sand over on a regular basis.
As far as cleaning algae off the sandbed goes, my astrea snails have done this from time to time, but hands down, I have two fighting conch snails which keep my sandbed spot clean. I have never seen algae form on my sandbed as a result and I have delt with my fair share of outbreaks. I've read about fighting conchs getting too large, but mine have been great... had em for about a year now without any problems.