Helpful links and tips for DotA 2 players old and new

Team Liquid: http://www.teamliquid.net/
DotA2 Liquipedia: http://wiki.teamliquid.net/dota2/Main_Page
Team liquid probably has some of the absolutely best DotA2 coverage(for e-sports) along with the DotA2 liquipedia which includes some stuff that the regular DotA2 wiki doesn't.
Such as being more focused around stuff like:
Recent tournaments: http://wiki.teamliquid.net/dota2/Recent_...nt_Results
It's essentially a bit more E-sport focused.

The DotA2 blog: http://blog.dota2.com/
News from valve about the game.
The DotA2 developer forums: http://dev.dota2.com/forum.php
Bug reports and so on.