Lily has updated the shop window to an autumn scheme: a collection of hardbacks notable for their colourful vintage jackets. In connection with that, Alan Hewer kindly provided us with some background about dust jackets, which didn't come into widespread use until the late 1800s. Nowadays, in book-collecting circles, they're viewed as integral to the book, but this wasn't the case prior to the 1950s, making vintage ones rare (and in many cases worth more than the book itself). There's more on this at Alan's website, Great War Dust Jackets, which focuses on his collection of jackets for books about World War I, often with striking cover artwork, published between 1914 and 1939. I've put a link on our main links page too.
If this topic interests you, there are a number of other good online collections: for instance, the New York Public Library's Digital Gallery collection of Dust Jackets from American and European Books, 1926-1947, Tom Swift Dust Jackets, classic crime fiction jacket artists, and so on - just Google "dust jackets".
Jackets are even a matter of controversy. Book buyers have to look out for facsimile jackets, often very well-made - but even with real ones, opinion is divided: is it acceptable that the jacket merely match the title and edition, or must it must be with its specific original book? See Dust-jackets: the debate at the Rare Book Society site.