Reddit and Hacker News, mostly. I check both several times a day and between the 2 there isn’t much left for anything else. As soon as something new or big happens, you’re going to probably hear about it on one of those 2 before other sites start picking it up from the source.
Hacker News:
https://news.ycombinator.com/news
Main reddit subs:
http://reddit.com/r/javascript
http://reddit.com/r/webdev
http://reddit.com/r/web_design
I follow a lot of others too, but most of the dev related content will be found there. Reddit is pretty nice, because you can get the top from the last X period of time.
http://www.reddit.com/r/programming/top/?sort=top&t=week
I’m not afraid to admit that I don’t understand the appeal or usefulness of Twitter. It seems like you would have to wade through a ton of junk for any useful content.