PlayDota

This is the website that has the most DotA knowledge. There are forums, guides, and other really quality content that kept the community going.

GosuGamers

GG.net is the #1 english dota coverage website. There is a betting system called GosuBets, replay storage, as well as tournament coverage and organization.

GG.net : Tournaments and Streaming

If you are looking to kick back and eat while watching someone else play go check out this site for stream lists as well as Vods and any ongoing tournaments

Dota 2 Wiki

All sorts of Dota 2 information... from the technical aspects of the game to contributions from the Dota community. See the PurgeGamers Wiki here.

Dota 2 on Reddit

If you are unfamiliar with reddit, I apologize for hurting your productiveness. Go to the Dota 2 subreddit for lots of great discussion, organizations, news, drama, and funny Dota 2 jokes.

Dota Insight

The Dota Insight Podcast is a longstanding Dota 2 Podcast that covers events in the scene every week. Hosts "Skythor", "LoudMetal", and "Finch" produce some great dota news, discussion, and learning content.