PHP would be a natural fit (Symfony2 or Laravel 4 (I'd vote for Laravel 4 as that is a rapidly growing market that is still relatively "poor" in learning material).
Also if you did happen to do it for Laravel 4, I'd buy it ;).
It's a truly excellent framework that pulls in the best in breed from the others but then puts a layer over the top that allows you to get things done (in a well engineered and testable manner).
The framework creator (Taylor Otwell) has an excellent book on leanpub and there is an amazing video guide site (laracasts.com) which is better than I have seen for anything (check out the free vids for an idea of quality).
Also if you did happen to do it for Laravel 4, I'd buy it ;).