For anyone new, now that we have the stream list at the top of the page, it may be worth getting to know some of the big names in Dota 2.

I'd say SingSing is my favorite. Just amusing to watch, even if he throws games a lot.
NaVi Dendi is probably the one who is the most reliably good player.
Merlini has a great stream. So does Purge. They both are very informative for new players by explaining the strategies behind their decisions.
And Tobi obviously streams great games with great commentary.

I also like pretty much any Team Liquid stream. I think LiquidTC is the most common. I am surprised they don't get more viewers.