I like http://www.sitepoint.com/ for comprehensibility, and Mozilla MDN https://developer.mozilla.org/en-US/ for accuracy.
Sitepoint isn't as in-depth as Mozilla, but it is far more comprehensible. MDN is a reference and that's necessary, but falls short on explaining details or difficult concepts. MDN also (of course) is targeted only to Mozilla's implementations.
WhatWG for HTML docs.
As far as CSS/JS goes I honestly just search and find something related to what I am doing. I'm sure others have some though.
I trust quirksmode.org, the bible of cross-browser issues.
I'm happy to see in his blog that he's been hired to copy all his tables to webplatform.org ! That's big news.