"21" (PG-13) Kevin Spacey, inset, offers a lesson to academics everywhere on how to beat the high cost of living. He plays a brilliant, greedy Massachusetts Institute of Technology professor who leads a team of math-whiz students (Kate Bosworth and Jim Sturgess among them), the gang developing a card-counting scheme to take Vegas casinos to the cleaners at the blackjack table. Single-disc DVD (Sony, $29), two-disc DVD ($35) and single-disc Blu-ray ($39) releases include three behind-the-scenes featurettes plus commentary by director Robert Luketic. The two-disc DVD set also comes with a digital copy of the movie for computers and portable video players.

"Doomsday" (R) Thirty years after a plague in Great Britain prompts authorities to seal off the island with a wall, the deadly virus emerges again. A military unit is dispatched into the quarantine zone to find a cure among the savage society that has sprung up among the British survivors. The DVD (Universal, $30) has the R-rated theatrical version and an unrated cut adding more footage, plus a couple of background featurettes. The Blu-ray disc ($40) has the unrated cut accompanied by cast interviews and behind-the-scenes material that can be accessed while watching the movie. Director Neil Marshall and some of the cast provide commentary on the unrated version.