For me it is Fleetwood Mac's The Dance, which brought Stevie Nicks and Lindsey Buckingham back into the fold, a decade after recording Tango in the Night. It's not really a hidden gem, as it was very popular, but if you like them and haven't heard it yet, give it a shot.
I remember watching the concert on TV and it was spectacular and magical, so the nostalgia goggles are firmly in place. I don't usually enjoy recorded live albums, but this one holds a special place for me.