Since you are interested in At Folsom Prison / At San Quentin: The 2 Classic Prison Concerts, here is a list of other items that you may find interesting.
Johnny and June Carter Cash
[ Sony & BMG Entertainment / CD - released 7/Feb/2006 ]
Partners in life and in song, Johnny and June had some of the best duets like "Jackson" and "It Ain't Me Babe", collected here for the first time.
Songs From the Inside (Digipak Edition)
[ Songs From the Inside / 2 CD/DVD - released 8/Jun/2012 ]
'Songs From the Inside' features songs by inmates at two New Zealand prisons and was produced by Anika Moa, Warren Maxwell, Maisey Rika and Ruia Aperahama.