Beyoncé - Star Search
Yes, Queen B is another Star Search alum. She and the rest of her girl group competed on the show but lost miserably. She was only 11 or 12 at the time, and everyone was shocked at her star power. Obviously, this was only a stepping stone into her career. She's one of the most famous singers in the world.
Jon Hamm - The Big Date
Sorry for this cursed image of Jon Hamm, but this is what he looked like during his time on The Big Date. This was a TV show literally just about dating. The show aired for one year, and Jon Hamm was the only good outcome of it.