What is the best language to learn at this moment?

I used to write html and was in a magazine way back in 1995. After joining the service and doing other things for the last several years, I have forgotten most of what I learned during that time period. However, I have constantly kept up to date with the user-facing side of technology. I would like to learn a programming language. What is the best language to learn, and in what way can I help and contribute in that language in 2013 and beyond? I used to spend hours coding html back in the day when I was a kid, and those were the best times of my life...I seem to have lost it, but the fire still burns.