Be careful with crayfish, you can't put a lot else in a tank with them (they'll eat your plants, fish, shrimp, snails, etc) depending on the species. But some of the more mild species and dwarfs are interesting if you want to take the chance (like Cajun Dwarfs, CPOs, CP sp. Shocko, Marbled, Appalachians). As for shrimp, Bamboos, Cherries, Tigers, Bumbles, etc are really neat looking. But as always, require some research before you purchase anything. And lobsters are strictly marine, so be careful of that... you can't mix species between freshwater, brackish and salt.