Most cruise ships will have some form (or multiple forms) of live entertainment on board, and you won't want to miss an opportunity to see it. Live entertainment options can include Broadway shows, live bands by the pool or in concert venues, or dinner and a show, such as Norwegian Cruise Line's
Illusionarium where dinner comes with a magic show.
Some of the world's best talent performs on cruise ships, and the smaller venues and crowds make it the ideal place to see performances. For music lovers, nearly every cruise will have live music available, from live cover bands and piano bars at night to locally-inspired poolside music.
Carnival also offers the Carnival LIVE series where bands such as Journey, Little Big Town, Rascal Flatts, and more have played on board for a small fee (much less than you'd paid to see them elsewhere). Some companies also host cruises specifically for music—think of a music festival at sea. If you're really interested in live music, those may be worth checking out.