My upcoming book, The Ruby Programming Language, now has cover art!. Here it is (hotlinked from amazon):
The birds on the cover are Horned Sungem hummingbirds. (Ruby-throated hummingbirds would have been nice, too, but these are beautiful birds and have "gem" in their name!) Here are photos showing the "horns" on the male and the cool-looking tail.
The Wikipedia entry has this to say about horned sungems:
The Horned Sungem (Heliactin bilophus) is a South American hummingbird, the only species of the genus Heliactin. The scientific name bilophus is sometimes considered a nomen oblitum, which, if accepted, results in Heliactin cornutus being the correct name for this species. It can achieve 90 wingbeats per second when it's hovering to drink nectar from flowers. A wingbeat is one complete up-and-down movement, which means that the horned sungem moves its wing muscles at a rate of more than 10,000 times per minute. It prefers fairly dry open or semi-open habitats, such as savanna and Cerrado. It avoids dense humid forest.
The book is nearing completion and I hope it will be available within one month of the release of Ruby 1.9. Pre-order it today! Your enthusiastic (I hope :-) pre-orders will help O'Reilly know how many copies to print. And amazon.com offers an additional 5% discount on these early orders.
Looks beautiful, David!