Sites like Microsoft's MSDN and Mozilla's MDN are not bad, as long as you remember that they view the world through coloured glasses. The only real reference is, of course, the W3C.
Whenever some site's information clashes with the information on the W3C's site, the W3C is always right.
Keep that in mind and you can safely peruse other websites, even W3Schools. W3Schools is not better or worse than other non-official websites.
