Many of your gobies do a good job of sifting the sand. I've got a orange spot that maintains the area around his den spotless.
Good Luck in your search!
I don't know the size of your tank but one of my favorites are the goatfish but if you want something to really sift then it would have to be a goby or blennie.
If I remember the name correctly, a banded sleeper goby would be a good choice to sift sand. I used to have one a year or so ago, and he would sift the CC all day long. It was a really active goby that would eat anything I put in the tank. So I imagine it would sift your sand really well... Maybe someone else on here can tell you more about them..