I found this awesome video on YouTube.
“Mary Did You Know” Preformed by group called Pentatonix
Pentatonix has that special a cappella swag, something that most singing groups tend to lack. They can sing, dance, harmonize and put together a respectable arrangement in just minutes. Mitch Grassi, Scott Hoying, and Kirstie Maldonado formed a trio during high school together in Arlington, Texas. They added the final two members, Avi Kaplan and Kevin Olusola, the day before their audition on Season 3 of NBC’s “The Sing-Off”, and PTX was born. They ended up winning “The Sing-Off”, and since then have been making strides in the music industry with their modern style and electronic sounds. Their debut EP, “PTX Volume 1”, was released on June 26th, 2012 and will be supported by their inaugural headlining tour this fall and winter.