1) Ray William Johnson
Ray William Johnson started out reviewing other videos that have been posted on the internet. His commentary on other people's videos quickly became very popular and he was at one time the most viewed person on Youtube!!! This is one amazing concept built on top of another amazing concept. He simply reviews other people's videos!!! He has since branched out into making his own music videos, scripted shows, a podcast, etc. He will be appearing in movies and perhaps have his own show one day. He's also a bit...vertically challenged...hehe.
Right about the same time, Ryan Higa, a.k.a. NigaHiga, was also wildly popular doing comedic videos on Youtube. He produces comedy bits where he plays different characters and does different types of voices. His brand of comedy is a combination of stand-up comedy, scripted skietches, and music videos. He started out posting some home videos he made with his friends in high school and continued to build his show from there. BTW, he's currently living in Las Vegas!!! Great choice!!!
Kevin Wu, a.k.a. Kevjumba, started out making videos from his bedroom. His style is a bit harder to determine. He does video blogs where he talks about different topics. He also does music videos and sketches. Some of his popular videos involve his dad, Papajumba, and basketball star, Jeremy Lin.
4) Wong Fu Productions
Wong Fu Productions is an internet video/movie production company started by three friends in college, Phillip Wang, Wesley Chan, and Ted Fu. They make sketches, web series, music videos, variety shows, interviews, etc. They cover many types of videos with quite a few of their videos dealing with relationship issues. They have gained international notoriety and do global tours of shows in front of live audiences.