Shadow of the Comet, the official Call of Cthulhu adventure game by Infogrames, is one of the best cosmic horror adventures ever released. It is an absolutely excellent offering that truly captures Lovecraft's atmosphere and a finely designed and wonderfully illustrated game you can find out more about here, here and here.
Oh, and you could actually own your very own boxed copy of the thing via this Shadow of the Comet (MS-DOS) eBay auction. It's the floppy version of the game and comes with five 3.5" disks, the manual, an Arkham Planetarium invitation and a fantastic collection of feelies. Seller ships worldwide.