I encourage you to listen to the entire episode or stream songs from the selected artists here.
If you're too lazy or busy to go to the ASC site, I've included a stream of one of All Songs's "biggest surprises." It's 'Please Read the Letter' by Robert Plant & Allison Krauss. (Plan on hearing this beautiful and subtle track repeatedly at a coffee shop near you).
Robert Plant & Allison Krauss - 'Please Read the Letter'