Lions, puffers, triggers, eels, wrasses, groupers, hawks, eels, and even sometimes large angels are all considered "aggressive" fish. However, you would just need to be careful mismatching between them. For instance, you cannot have a trigger with a lion, and I would not recommend a puffer with an eel. Also remember, somethings, like groupers and wrasses can only go one to a tank.
You really need to post fish you like and then we can go from there though. You can have all kinds of different fish in a tank that size.