The Bobs perform Psycho Killer (Talking Heads)
In a White Room (Cream) performed by The Bobs
The Bobs are an a cappella group originally from San Francisco, where the group formed in the early 80s, and now located in Seattle. As you can tell from the two videos, the members of the group have changed over the years. For more information, go here.
They also have their own website.
Yes, as difficult as it is to believe, they do perform without musical instruments perfectly mimicking their sounds. My favorite is In a White Room.
Hope you enjoy The Bobs.