18. Devon Murray - Seamus Finnegan
Devon Murray is one of the former child actors who was with the Harry Potter franchise from the very beginning. He played Seamus Finnegan, the Irish bloke who was one of Harry's best mates, and had a habit of blowing things up. But although Devon Murray was featured in every single one of the Harry Potter films, for whatever reason his success in the franchise hasn't translated itself into more roles. Harry Potter and the Deathly Hollows, Part II, is the last credit he has on his IMDB page, with nothing else in the pipeline. Earlier this year, he gave an interview with SnitchSeeker discussing a pilot that he's working on, a sort of Father Ted type show, that supposedly began filming in June. So only time will tell if that pans out.
17. Josh Herdman - Gregory Goyle
Unlike his Slytherin counterpart played by Jamie Waylett (who is currently serving time for his illegal actions during the 2011 riots), Josh Herdman has largely stayed on the straight and narrow. He played Goyle, one of Draco Malfoy's knuckle-dragging henchmen, and was featured in every Harry Potter film (as well as Thunderpants, Rupert Grint's breakout film that he'd probably like to forget ever happened). Since the end of the series, he's continued to find small parts in a number of films, including Common People, Piggy, The Estate Film, and the upcoming drama Wasted. Herdman has a very specific physical type, which at the moment limits him to a certain council estate, rough-and-tumble sort of character, but we'd genuinely like to see him find continued success as he grows older.