As Craig mentioned sexy shrimp are a good option. A Pederson's cleaner shrimp or glass anemone shrimp might also be a good choice. I've had people recommend bumblebee shrimp to me, but I've never kept them myself. I think you could get away with a pair of shrimp and a couple snails without overloading the tank.
With the lighting you are fairly limited. Mushrooms and zoanthids would be good choices and come in lots of colors and textures. I've got a little xenia frag in my 3 gallon that seems to be doing well, so that might also be an option to add some motion.