Ever played Dark Seed? It's on my 'to play' list, though I'm not really fond of horror games. Still, it's Giger. I should get around to it. I don't think he worked on any other games, though. His Wikipedia page says that too. However, there are plenty of Giger-inspired images, cover arts and such out there. Nox Arcana's Necronomicon comes to mind: It's not the best in the bunch, but that cover has plenty of elements characteristic for Giger's works.