Eugene Pallette—best known for his froggy bass voice, this veteran of such films as My Man Godfrey and Mr. Smith Goes to Washington made his first movie in 1913 and had an important role in D.W. Griffith's classic Intolerance.
Adolphe Menjou—debuting in 1914, he was already great in such silent films as A Woman of Paris and The Marriage Circle, but sound added another layer of smarm and good humor. See, e.g., Morocco, The Front Page, A Farewell to Arms, Stage Door, Paths of Glory, etc.
Wallace Beery—a ham in any age, he played supporting roles in the The Last of the Mohicans (1920), the Douglas Fairbanks version of Robin Hood (1922), Buster Keaton's Three Ages (1923), and The Lost World (1925), but he won an Oscar in the sound era.
Mary Astor—made her film debut in 1920, but did her best work in Dodsworth and The Maltese Falcon, and won an Oscar for The Great Lie in 1941.
Lionel Barrymore—debuted in 1908 and was excellent in the Gloria Swanson version of Sadie Thompson but is best known for such sound work as It's A Wonderful Life, Key Largo, Grand Hotel and his Oscar-winning role in A Free Soul.
Marie Dressler—she starred across from Chaplin in the first feature-length comedy, Tillie's Punctured Romance in 1914, became a supporting player, then virtually disappeared before becoming Hollywood's top leading lady (no, seriously!) in the sound era, winning an Oscar for Min and Bill and providing the best double take in film history opposite Jean Harlow in Dinner at Eight.
Carole Lombard—debuting in 1921, she made multiple brief appearances as eye candy until Howard Hawks had the good sense to cast this irreverent, salty-tongued goddess in a comedy, 1934's Twentieth Century. After that, we got such classics as My Man Godfrey, Nothing Sacred and To Be or Not to Be before her untimely death in 1942.
Myrna Loy—played dozens of largely-forgotten vamps and exotics between 1925 and 1934 until cast opposite William Powell in the classic comedy whodunit, The Thin Man. After that, she was one of the biggest stars of Hollywood's Golden Age, a leading lady to the likes of Clark Gable, Cary Grant, Fredric March and, of course, Powell with whom she made fourteen films.
William Powell—Roger Ebert once wrote that Powell was to dialogue what Fred Astaire was to dance, and with the coming of the sound era, his career blossomed. But you can see him in thirty-five silent films, mostly as the stock heavy (including a brilliant turn as a Russian revolutionary in Josef von Sternberg's The Last Command.)