I'm a novice to Bluegrass but I have a CD by The Bluegrass Cardinals I like a lot, I think it may be a best of.
This is Folk more than Bluegrass but if you don't own The Weavers Live At Carnegie Hall, you should check it out, great sound and performance. I'm not a big Folk fan, at least I didn't thik I was, LOL, but I do like this album. I'm talking about the earlier one, don't remember the year, they do have two, I haven't heard the later one. As a side note, the last remaining member passed away recently.
More of a novelty, ever hear Hayseed Dixie? They do Bluegrass versions of Rock music, some of it is pretty good but the recording SQ isn't so hot.