Your inverts, as someone else has already stated, depend completely on what you have in the tank. If it is an aggressive tank, you probably would be wasting your money in getting inverts. If you have a community tank, you should be able to get away with several different types of shrimp (cleaner shrimp, peppermint shrimp, fire shrimp, camel shrimp), crabs (anemone crabs, porcelain crabs, emerald crabs, hermit crabs), and snails (Mexican turbo snails, nassarius snails, astrea snails, etc...).
Post your stock list and you will get much more useful recommendations.