Ace doubles: Pulp-lover's dream!

I just got in a stack of old Ace Doubles, and wanted to share some of the awesome cover art with you all, because it's too much fun to keep to myself. :) Each Ace Double has two novels in it, and many sci-fi classics started out in this format back in the 1950s or thereabouts. The novels are printed back-to-back. Each book has one of the covers to itself, and the story reads front to back from that side of the book, which means to read the second book, you have to flip the book over and then turn it the other side up. Kind of a cool idea, really!

Here is a sampling of typically wonderful intergalactic art from them.  If you click on the image, you will be able to see a larger version of the picture.

Ace D-162

Ace D-227

One side of Ace D-99 -- with tentacles!!!

To get an idea of how many books were published this way, take a peek at the list on Wikipedia, here: http://en.wikipedia.org/wiki/List_of_Ace_double_novels

While the series is most famous for its focus on the field of science fiction, Ace also spread its range to include other genres such as Westerns and mysteries.