I have recently discovered a CD titled Bluegrass that Swings by David Naiditch on the Airplay Direct Website. David Naiditch is a harmonica player who plays Bluegrass music, Western Swing, Jazz, Klezmer, Ragtime and more.
The harmonica is not the typical Bluegrass instrument, it was the first time that I found Bluegrass recordings with a harmonica. But it fits well to a typical Bluegrass band with guitar, banjo, fiddle and mandolin.
David has compile a Bluegrass playlist with more than 43 videos, including many examples from his CDs.
Bluegrass tunes – Playlist by David Naiditch
But I remember that Bill Monroe used to have an accordion in some of his early recordings like in this recording of Blue Grass Special at the end of the video:
Sierra Hull is the mandolin player in the following video of Old Dangerfield: