www.senseis.xmp.net/
This is a go player's wikipedia. It is not perfect, but it is the best we have and is packed with information.
Video lectures (there are a lot to chose from, so just to cover the basics...)
Nick Sibicky
Great guy, publishing actual lectures from an American Go club. I think these are great for beginners.
Dwyrin
A famous high dan player with highly regarded "Basic series" which focus on the fundamentals. Might be good knowing a bit already before watching.
Official AGA channel
Probably for those at least around Single digit kyu level. Hosting reviews by the absolutely phenomenal Micheal Redmond (9p).
Sunday Go Lessons
Posting translated commentaries from Japanese title matches. Go watch Cho Chickun.