Some may not know that "When Worlds Collide" is based on a 1932 novel by Philip Wylie and Edwin Balmer. What fewer seem to know is that in 1934 they published a sequel novel, "After Worlds Collide." George Pal, producer of the film of WWC also wanted to make a film of the sequel, but according to imdb, the failure of his 1955 film "Conquest of Space" blew his chances.
It's also a little known fact that a movie of "Logan's Run" was almost made in the late 60s by George Pal. The project fell through.
Something I didn't know...apparently in STII:TWOK, there are two crates in the Genesis cave labelled "Bellus" and "Zyra."