With 18 seasons in the books and a 19th on the way, hit procedural "NCIS" is still going strong. The immensely popular CBS series remains one of the most-watched shows on television. In fact, in its 10th season, it even surpassed "Sunday Night Football" and "American Idol" to become the highest-rated broadcast on network TV, according to TV By the Numbers and it's never left the list of the top three most-watched shows since that time. With nearly two decades worth of episodes done, plenty of guest actors have appeared on "NCIS." Some appeared on the show as a precursor to their fame, such as Zac Efron and Abigail Breslin, while other well-established actors have shown up to spend some time with Agent Gibbs (Mark Harmon) and Co., like Jamie Lee Curtis and Lily Tomlin.