This is derived from the O'Reilly State of the Computer Book Market survey. I highly recommend reading the whole article, and Tim Bray's take on the situation.
I find it interesting comparing the difference in units sold vs. titles available. There is an inherent lag in commissioning a book and when it gets published. Thus, we can assume that if the number of titles greatly outnumber sales, that programming language is declining in popularity, and vice versa. By this measure:
I was particularly interested in the strong showing of JavaScript, given my JavaScript shell & servlet host Askari.
