I'm using IPython Notebook. It has its pluses and minuses. The pluses are all code is inline, and you don't have to worry about having to keep things in sync (change the code for this plot, make sure the output gets named correctly and copied to the right place in the book). LaTeX is supported. It is easy to do animations with either javascript or Python. It is a very hackable platform. nbviewer.ipython.org will serve a static version of your book (it accesses it from Github, it does not store it on its servers).<p>Downside is it doesn't have the concept of 'books'. No chapters, etc. PDF generation is clunky at best. There is currently a version 3 in development that is changing the format of the ipynb format. It only supports Python, Julia, and Ruby as languages right now (but it turning into the Jupyter project with plans to support many more). You are kind of on the bleeding edge.<p>Mostly I like it, but I do wish there was more support/concept of books vs notebooks.<p>edit: This is not a recommendation; I did not survey all of the options. For me the mix of executable code and text and LaTeX in one document was a killer feature. That may be irrelevant for your book.
I decided to go with Leanpub. I really like it's philosophy of making it easy to push updates, which I consider particularly important to a technical manual. And of course, being able to write everything in markdown and push to a private Github repo to start a new version suits me like a glove!