Java is one of the biggest most fundamental languages around. As Oracle loves to point out more that 5 billion devices run Java. Java, created in 1995, has become the defacto standard for a lot of programming out there. Its the language Google chose to make Android apps in. Though a lot of people complain about its verbose script and strict adherence to the rules, the truth is its popularity and power make it one of the languages to learn.
P.S. I read in a few places that Java seemed stagnant compared to modern languages, which just isn't true. The new Java SE 8 launched March, 2014.
Javascript is another de facto standard. This one is for running client side on the web. It runs on nearly every browser and is used in the majority of web applications (move over Google Dart). One of the interesting things about Javascript is that it is functional programming and an interpreted language. Javascript would perhaps not be the best language to learn functional programming with but it is definitely a must know lanuage for its prominence on the web. Now, however Javascript is really showing off with a new system called NodeJS, which lets you create Javascript programs that can run on your computer. The beauty of this is you can now have server side scripting (and indeed your entire web stack) in one language. This pips Javascript up in the must know list of programming languages.
Ruby was created in 1999, and purported to be a mix of functional and imperitive programming. Ruby is all about simpler faster syntax, that allows you to code quickly. It supports metaprogramming through reflection and has a bunch of really awesome features. Ruby is also about Ruby on Rails which is a popular server side framework for website programmers.
apart from PHP, Python, Scala, Clojure
Languages I want to know better
C is one of the most widely used programming languages of all time. It is used even now to program Adruino boards and other high level sytems. While it might not have the support for many features C gives you a unique perspective in terms of where computing came from and what it can be used to do.
LISP is an old functional oriented language today that is popularkly used in AI research. The reason for its popularity is its ability to be
Which is fancy speak for it can be used to edit its own programs while running. LISP is an old language and is not often used in practical software but as a computer programmer LISP is definitely a thing to know