All of them. It's more important to learn paradigms than to learn just a language. Each language will forcibly teach you new paradigms which you can then use when writing in other languages. Knowing both Python and C, for example, makes me a better programmer in both languages. It also lets you choose which language will most easily meet the needs of each task, and even open you to the possibility of mixing languages in different areas of one project.
Adding on to this, it is also good to learn more than just your standard programming languages. Having a good, working Unix knowledge goes a long way in making your life easier. Tools/languages that I would recommend getting intimate with are awk, sed, grep, ack, make, and general shell scripting. These tools have helped make my life as a programmer so much better, and saved me countless hours of repetitive tasks. Also, keep in mind that you don't have to learn everything mentioned in this thread all at once. You can spend years learning them. :)