Paul Brady's Missing Liberty Tapes is at the top of my list, mentioned earlier in the thread and well worth acquiring. Terrific energy, a historical time capsule of traditional Irish music in Dublin in 1974.
I second the nomination of Geoff Muldaur's Beautiful Isle of Somewhere, recorded live in Germany Geoff though the audience was rather cool to him, just a cultural phenomenon, fun to hear him muttering Danke Schoen bewtween songs. This appearance is what brought him bacl out on the road, and I am glad of it.