The Children's Choice Book Club was a wonderful mail-order book club run by Scholastic from about 1960 until approximately 1990. I was fortunate enough to be a member for a few months - the books that arrived were always hardbound and had unique little touches. I don't remember very much about the process of the Club itself, or how the books themselves were shipped to the members. But fortunately for us, there are bits and pieces of ephemera bound into some of the books themselves, so we can reconstruct parts of the puzzle.
Part of the charm of these book club editions was the lovable little furry monster that was plastered all across the books - on the spine, in advertisements, and even on special bookplate pages:
The monster wasn't the only special touch added to these editions. All of them featured a special rainbow-colored spine. That's made it rather easy to identify books published by the Club then and now. If you get a collection together, the spines wouldn't line up (the books weren't published to the same size - and even the ones sized the same didn't always have the colors lined up). This was an eye-catching feature, especially for the target market - young children:
As this was a book club - these editions are not always in high demand. First editions and regular editions of the works are usually preferred by most people. However, I by far prefer these editions due to their charm and being part of a "series" by having a common feature of the rainbow spines. They also selected high-quality books dating as far back as the 1920s, and published new editions right up to the late 1980s. All books share some common features (as noted above), plus the original book covers are set in a matted frame on these editions. No dust jackets were ever issued.
Most of these books can still be had for less than a song. Some unique books due to their subject matter or general availability can fetch much more than a regular book would. Leo Lionni's books, Where The Wild Things Are, It's a Mystery Charlie Brown, and The Red Balloon are all some books that can fetch a premium. But as always, it depends on the book itself and the seller.