WarmWasp's a great name. Sadly squashed before his time. Anyway, I like the commentaries on Knowing Me, Knowing You and I'm Alan Partridge. Sadly like the DVD itself, commentaries seemed doomed to extinction.
Favourite DVD Commentaries? Page 2
The commentaries on Joking Apart give great insight into the series (and the camaraderie between Moffat and the cast really is fantastic). The Father Ted ones are great, especially if you're thinking of getting into comedy writing (leaving aside all notions of what Linehan has become as a human being). Spaced I remember being very entertaining too.
It's not a comedy but the actors commentary on the 70s version of The Tomorrow People is really funny