It is well documented that Halloween, Halloween II, and The Thing have alternative TV scenes, but not much is discussed about his other films.
For instance, when I was traveling a few years back, I saw Prince of Darkness on TNT (IIRC). It had extended shots, which included extra book passages on the Brotherhood of Sleep. These scenes aren't on the R1 or Momentum R2 DVDs. I didn't watch the entire film, but IMDB lists a few other differences.
In addition, Mitch/Old Biff's defunct site listed The Fog TV version. I have been unable to find any info on the differences between that and the film version.
I'd be interested to find out if there are an extended or alternative scenes for John Carpenter's other films.
I hope The Thing and Prince of Darkness TV versions are preserved as well.