Here's a few off the top of my head. Some may not appear to be bluegrass songs but you'd be surprised. Some are fiddle tunes.

Girl I Left Behind Me
Froggie Went A-Courting
Handsome Molly
Garry Owen
Cuckoo
Danny Boy (covered by Bill Monroe)
Hog-Eye
Hop High Ladies
Irish Washerwoman
Acres of Clams
Dear Companion
Blackberry Blossom

We went over the Drowsey Sleeper songs in the East Virginia thread- songs from that are: Silver Dagger/Katie Dear, Greenback dollar, Man of Constant Sorrow, Dark Hollow, Awake Awake/Arise Arise, In Old Virginny, and Dear Companion/Lover's Farewell songs.

-Richie