Google - Goes without saying, I always start my search on Google. While many times it ends up leading me to the same sites (most are listed below), it is far better at finding the information I need than using those sites' built-in search directly most times. If you do know what site you're going after, simply google your search term followed by
Stack Overflow - Have a more specific programming question? stackoverflow.com is your friend. But please make sure no one has asked your question before you ask it. Most likely someone has. As a matter of fact I spend a huge amount of my day as a dev on SO, and I have yet to post a single question on it. There's always been someone who's already asked my question before me. Keep that in mind.
Stack Exchange - Stackoverflow is part of an entire company called Stack Exchange. They have other sites that could be useful for you. Particularly serverfault.com for all your server related questions, askubuntu.com for your Ubuntu (Linux distribution) questions, superuser.com for other advanced features of your OS, and many many more sites for basically most of your tech questions.
Quora - For more fluffy stuff like "how is it to work for Google?", "What should I do to prepare for an interview at XYZ?" you should check out quora.com.
Learn X in Y Minutes - A good place to get an initial overview of a language and where I normally start the journey that is learning a new language: learnxinyminutes.com.
GitHub - Another place you should become familiar with (eventually) is GitHub. github.com is the place to find open source software. Most devs today (at least web developers in the US) have a profile on GitHub and use it to showcase their work. In other instances, they use it to just collaborate on software development. At my company, for example, we use GitHub heavily to review each other's code and to keep track of changes. Other than that it is literally a hub for Open Source Software and my go-to when I try to find a library that does something I need (if I don't want to build it from scratch).
Mozilla Developer Network - I use this site for all documentation web related. Whether it's ECMAScript, HTML5, or other web standards.
HTML5 Rocks - Where I read about a lot of new things JS and front-end related
Google's Web Fundamentals - I come here to learn about web fundamentals, duh.
Other places you should probably be familiar with, although they are more part of nerd culture than requirements:
Hacker News - The site where I get most of my tech news. It is a simple and noise-free site where people post worthy links and articles related to the tech industry. You will find articles and discussions about code, startups, and other techy things.
Reddit - Where I also go to hear about new products, ideas, and news.
Twitter - It is how I get all my news, to be honest (some of my friends use Snapchat for their news so don't judge). But Twitter is a great place to follow industry leaders. I, for example, follow some major JS and front-end developers. Every now and again they post interesting articles, talk about cool conventions, and keep me up to date on new technologies.
Obviously there are a bunch of other sites out there where you're going to be spending your time researching and learning. Each technology, language, and industry have their own preferred tools, but the ones above are where lots of web developers spend a lot of their time.