As Arlinda commented on my Mama Tried post - I was first a fan of Bearfoot Bluegrass. Saw them at a show at the Birchmere sometime last year. They are a much younger band than Mama Tried and possess not one banjo - a shock for the stereotypical view of the genre. However, they still impress with their masterful mandolin-violin combination and sweet harmonies.
I like so many of their songs but chose to highlight just two here to try to you give a feel for them. The first, Molasses, is a little more of what you expect from a bluegrass band - an upbeat tune. The second, Billy, is an acappella one that always makes me stop what I'm doing when I hear it.
I am FAR from knowledgeable in bluegrass but enjoy these two bands - but don't ask me to pick a favorite.
Bearfoot Bluegrass #1 - Molasses
Bearfoot Bluegrass #2 - Billy