I absolutely love sexy shrimp.. A nano of that size would be ideal for viewing them, too.
If you're going for a sand bed, nassarius snails will be sure to show up well despite their small size and it's always fun to watch them pop up during feeding time.
Fishwise there aren't many fish I'm comfortable putting in a tank that small. Clown gobies are about the only fish that seem like a good idea to me. I'm half tempted to try a clown in anemones in my nano (it's 5G as well) but if she doesn't host then that's not much room to pace back and forth.
