I can't recall the exact path I took through the internet tubes to find it, but I recently became aware of the immense library of free music available on archive.org, the Internet Archive. They have an incredibly long list of live music performances. There's a special section just for Grateful Dead bootlegs. My first random click on the long list of live performances landed me listening to a band called Hayseed Dixie. It's a great down-home country bluegrass concert. I've listened to the whole concert now, which includes some rock covers. I love bluegrassified covers of non-bluegrass songs. By far the song that will be hardest to forget is this gem, entitled, Keepin' Yer Poop in a Jar. Download or listen to it in the player below. Or listen and/or download the entire concert.
Hayseed Dixie is a sophisticated group of gentlemen if I ever saw one. Hard to tell which one is Cooter and which one is Kletus. (photo via 3cardtrick.com)
No matter what your musical taste, there's bound to be something you like at the Internet Archive's Live Music Archive section.
Oh, and it's all 100% legal. The artists have donated their work.