I know 16 languages, actively use 5, and expect to learn at least one every year or two for the rest of my career. Advocating one programming language over another is a bit like saying that a hammer is better than a screwdriver.
My suggestion is to find a cool project and then learn the language that is most appropriate for that project. The most important part is to understand how and why the new language is different than the ones you already know.
Otherwise, you can freely download "How to Think Like a Computer Scientist" from
http://www.greenteapress.com/thinkpython/ . I'm a bit biased, as the author was one of my professors, but it may be one of the easiest ways to learn the important high level concepts. It also happens to be one of my favorite education stories - Alan learned Python by reading his own book on Python... He wrote the text for Java and open sourced it. Someone downloaded it, translated it to Python, and sent it back to him. Voila! He learned python by reading his own book!