shrimp - skunk cleaner, peppermint, fire. i'd stay away from a banded in that small of tank, they can be destructive if crowded.
maybe a small sand sifting/serpent star (not the green one)
snails are good... i don't like crabs at all. i have witfull to thank for that. i have two scarlet hermits that have disappeared in my tank... i feel they are secretly plotting against me... i'm waiting for a coup de-crab to occur.
things like anemones and clams you'll have to wait a lot longer before adding... and they need a lot more light, and clams will outgrow the tank.
i'd stay away from seacucumbers, and the like... some of them can nuke your tank if they die.
fish!
percula clowns (pretty much any but the maroon yellow striped, they get too big)
any kind of goby, the goby/pistol shrimp pair is cool too
firefish (need the lid closed, they are jumpers, but very cool looking).
this is a great guide
http://www.liveaquaria.com/product/s...fm?pCatId=2124