Will Fuller being the obvious.
Still, he also developed TJ Jones, Equanimeous St. Brown, who had a very good year in 2016, along with Torii Hunter Jr. (on his way to a very good season in 2016 before a cheap shot ended his football career. Corey Robinson was also a pretty solid player as well. I'd even throw Chris Brown in there, since he was a very solid option at WR2 for us.