For front-end development, you need HTML/CSS/Javascript. There's not really any way around that. Yes, all of them are languages, just perhaps not *programming* languages.
For back-end development, it depends on your needs.
PHP: Widespread, supported by just about everything, but terribly inconsistent, and generally a poor language/platform.
Python: Strong focus on 'correct' and reliable code, but poor documentation, and HTTPd support is not as good as it should be. Somewhat hostile community.
Node.js: Server-side Javascript. Good documentation, good platform, but not very widespread (yet). Uses prototypical inheritance, which is different from the classical inheritance that most other languages use. CoffeeScript can be used to make it faster to write.
Ruby: Supposedly makes writing code really fast and easy, but I've never really seen the point of it personally. Known for using a lot of resources and having pretty awful version management, primarily.
Here's a comparison chart:
https://docs.google.com/a/cryto.net/spreadsheets/d/1Z0ZQUH3EwTzCF0jJUN5eQZ1P7UFz3gJgjbMFoVDyjfk/edit#gid=0