The Thing from Another World is a 1951 film believed to have been directed by Howard Hawks. James Arness is in this film as The Thing. If you listen to the video's host you'll hear the Star Trek connection. I like the music in this one.
"Watch the skies!"
This video is introduced by commentary from a host, which is quite interesting. The movie itself starts at about 7:54, and commentary resumes at about 1:34:24:
1000 Misspent Hours calls it "the world’s first alien paranoia movie, the film that spawned the entire “commies from space” sub-genre in the 1950’s". Moria agrees it's " the very first alien invader film" and "one of the best." Slant Magazine says, "The Thing From Another World's titular vegetable creature may not have the cache of a Freddy or Jason, but there's no denying that this chilling Hawks production is a must-see for science fiction and horror aficionados." Only the Cinema has a post.
4/5/2009: SFSignal is featuring it in their Sunday Cinema post.
5/26/2009: Ferdy on Film has a review.