I have first heard of Samuel Tsui earlier this year when I heard his rendition of "Fireflies" by Owl City and since then he has been a household name in Youtube for covers and mashups. What's more wonderful is that he does eveything in his renditions. Aside from the vocals, he is involved in the editing, guitars, pianos - name it and he can do it. He's one hell of a performer and very good at it.
This is one of the more recent covers by Sam. This is a mash-up of 3 current big hits - Eminem and Rihanna's "Love The Way You Lie", Taio Cruz and Ke$ha's "Dirty Picture" and Katy Perry's "Teenage Dream". And he does all of these versions in the best way possible. Truly mesmerizing. Sam Tsui is one of the best out there and hope he'll continue doing wonderful music.