[Utah-astronomy] Where to buy large astronomy photos or posters

I'd love to get a large poster or photo of, perhaps, the Andromeda galaxy to hang in my living room. By large I'm thinking around 32 x 24 or larger. I realize that the more the picture gets enlarged, the less sharp it can be, so I wonder if any of you folks have ideas where to look. I'll try the Clark Planetarium (they said they don't have many) and I found a site on the web, allposters.com, that looks good, but I don't know how they would actually turn out to be . Any suggestions?