'The 27th Day' now on DVD
Sinister Cinema has recently released THE 27TH DAY on DVD, in a good print. Until (and if) Sony/Columbia comes out with its own DVD, SinCin's should be quite acceptable for anyone looking for it. (Go to sinistercinema.com -- also check for sales, which they run fairly frequently).
I've also seen this available from scifistation.com but have no experience with their products.
UPDATE -- 8 years later.... The SinCin DVD has long been discontinued but the film is available directly from Columbia, on a Mill Creek DVD release of several sci-fi films, as well as a separate disc from their Sony Classics MOD line (from which all the Mill Creek films in that set have been taken).