Assuming it is not a sharp sand like builder's sand a few Corydoras would be a good addition. They are always digging around in the sand looking for bits of missed food. If you do have a sharp sand you probably want to stay away from Corys, the sharp sand wears down their barbels and since they pass a lot of sand through their gills it will also cause gill damage in an amazingly short time. There are quite a few different species of catfish that are quite active at the substrate level of an aquarium, check out
www.planetcatfish.com for more info. You would probably want to stay away from any of the larger catfish though, they can be rough on a planted tank.
I have one 10 gallon tank with a lake sand substrate, nice and gentle for the Corys. It is a planted tank and I have two corys (had three one died, waiting to see if anything else dies before replacing it), a clown pleco, a small spotted raphael who is waiting for its real home to stabalize, and two banjo cats - at least I think I still have both of them, they dig down into the sand and I go for months without seeing them. I like the lake sand substrate. I have never had any troubles keeping it clean thanks to the Corys stirring it up, and it doesn't seem to pack down like builder's sand would.. Last time I was up to my parents home I picked up a couple more tubs of the stuff. I want to set up a larger tank with a sand substrate and see how some Geophagus like it.