A Sand Sifting Cucumber did wonders for the sand in my tank. They are very peaceful and eat sand all day long. They also poop sand which is funny to watch! Ok that was a little gross!
Mine does a great job of covering the entire tank and cleaning the sand. Unlike some others, they don't make a big mess or shift the sand around a whole lot. Basically it goes in one end dirty and comes out the other nice and clean. They also only "eat" the top layer of, so you don't have to worry about them messing up the bacteria load of your live sand.
Someone will probably post and say they can poision your tank if they get scared, eaten caught in a filter, etc., but there are just as many reports that say that is not true. All I know is I love mine and would encourage anyone with less than clean sand to get one.