That depends on why you are looking to learn a new language. For most web development projects, PHP is fine. If you are looking to learn something totally new

That depends on why you are looking to learn a new language. For most web development projects, PHP is fine. If you are looking to learn something totally new, why not go for something like Smalltalk, Erlang, Lisp or some other language that's quite different from Ruby, Python and PHP?. If you are looking to learn something that will help your web development skills, then make sure you are very strong with Javascript and a framework such as Jquery before looking to other languages.