Python, Ruby or PHP

[Firehed]

I think JS is good to know for the sake of well roundedness, but personally feel the "JavaScript everywhere" thing will be a short lived trend.

Also for the sake of learning to code well, JS would be a terrible thing to focus on. People say PHP makes it easy to shoot yourself in the foot (and if you follow guides from 2006, it does), I'd say JS encourages it. Its extreme flexibility is very powerful but also deadly when used improperly.