Having just read S. Peter Dance's quirky Out Of My Shell, I decided to revisit my probably-too-extensive shell library, beginning with a few of Dance's other books.
Far from the most attractive or user-friendly shell guide - text is small, photos are clear but boring, and the arrangement is confusing unless you are really up on your molluscan taxonomy - this is certainly one of the most…well, encyclopedic (hence the name).
So if you do have a shell that you're trying to identify, this would be the preferred first place to go. But if you just want to browse a pretty book, there are a number of better choices.
The Collector's Encyclopedia of Shells by S. Peter Dance (McGraw-Hill 1974)(594.1477) is a beautiful compendium of shells from around the world. My rating: 7/10, finished 2001.