Commentaries to avoid because of spoilers.

  • Angel: spoilers for episodes in future seasons.
  • Buffy the vampire slayer: spoilers for episodes in the rest of the seasons, future seasons, and spin off series. There are even spoilers on images on the DVD menus.
  • Dollhouse: 1.13 Epitaph one (2009) commentary spoils Dr. Horrible's sing-a-long-blog.
  • Frasier: 2.03 "The matchmaker" has spoilers for a future season.
  • Stargate Atlantis: 4.08 "The seer" has spoilers for the rest of season 4, season 5, and Stargate: The ark of truth.
  • True blood: seasons 1-3 commentaries contain major spoilers for future episodes of those seasons.
  • True blood: 1.05 contains spoilers for the end of Six feet under.
  • True blood: 3.04 spoils Big love.
  • Twin peaks: according to a metafilter thread.
  • The wire: season 1 commentaries contain major spoilers for future seasons including 5 according to an IMDb thread - unconfirmed.
Author Comments: 

After Firefly was cancelled, I gave away my TV when I realized that I'd rather be watching ad-free DVDs with special features. The problem is that many commentaries are made by people who assume the DVD watchers have already seen the entire series or season, so if you're renting individual DVDs you'll oftentimes get burned by spoilers for future episodes or seasons you haven't rented yet.