Commentaries to avoid because of spoilers.

  • Angel: spoilers for episodes in future seasons.
  • Buffy the vampire slayer: spoilers in commentaries not just for episodes in the rest of seasons, but also for future seasons and spin off series. There are even spoilers on images on the DVD menus. Also, some of the episode order layouts are not clear.
  • Frasier: 2.03 "The matchmaker" has spoilers for a future season I haven't seen.
  • Stargate Atlantis: 4.08 "The seer" has spoilers for the rest of season 4, season 5, and Stargate: The ark of truth.
  • True blood: season 1 and 2 commentaries contain major spoilers for future episodes of those seasons, and 1.05 contains spoilers for the end of Six feet under.
  • 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.