If you want a job with a Fortune 500 company, Java or C#/.NET, probably.
If you're looking more at start-ups and smallish dot.coms, it's pretty much all over the place. PHP is always around, but Ruby/Rails devs probably make more money -- if they're good. NodeJS is gaining a lot of traction lately, but no idea how pay compares. Python is big if you get more into the data analysis side of things, but not so much for typical web site development.
Your mileage may vary, particularly by geographic location.