Talmudic tradition tells us not to look at the vessel but at what it contains, and that is certainly sound advice on one level. However, I have always been fascinated by beautiful vessels of all kinds - not least bookbindings, which are perhaps more closely bound up with their contents than other types of vessel.
With a tip of the hat to Mirabilis (a consistently fascinating Blog) for the reference, here is a link to an online exhibition of beautiful Hand Bookbindings from the Special Collections in the Princeton University Library. The display is large and varied, including leather bindings of many kinds, marbled end-papers, gold tooling, and much more.
Just to give you a small taste of the riches on view there, here is an example of "gauffered edge-work":
However, my personal favorite category in this field has long been "fore-edge painting", a secret art in the following sense. When you see the book it looks as though it is merely gilt-edged. Only when you fan out the pages slightly - not too much now - does the painting appear. Here is an example of a fore-edge painting of an English village scene.