(X)HTML and CSS. While you learn those, become intimately familiar with this document - http://www.w3.org/TR/WAI-WEBCONTENT/
That's basically it coupled with some forethought on what kind of 'good web developer' you wish to become. I agree with this post and the order Farkas put them in .
I agree as well. html is the most basic thing to learn, and should be learned formost. With a good knowledge of html and css, you can do just about anything. There are thousands of free scripts out there to get you by until you can grasp php and sql.
I recommend any of the FriendsOfEd books: Web Standards Solutions: The Markup and Style Handbook Designing with Web Standards Bulletproof Web Design These are just a few.