Rescue - a christian a capella quartet. Their music can be purchased only from www.rescueministries.com

Album Listing -

1.Rescue
2.Rescue - 2000 years ago

Not a religious person myself, I was caught by their incredible tone and sound quality. Unfortunately, they are not well known, and therefore hard to download. They do have a small amount of support from mp3.com though so you can hear them for free there.