I listened to the first 4 seasons of Red Dwarf's commentaries and a couple episodes of the 5th. I ended up stopping because of burnout, but I've been intending to keep going at some point. It's fun hearing the cast play off each other in real life and there are a lot of cool anecdotes and trivia in there.
I've also watched the commentaries of the first season of Torchwood. I didn't think that much of it, it was just a different way of watching the same episodes again.