Well to be great and most importantly, competitive, you need to know: XHTML (HTML but with stricter rules), CSS, JavaScript, PHP and perhaps Flash. But there's so much more you could be learning as well.
Here's a few useful sites to learn the basics:
http://www.w3schools.com/
http://www.lynda.com/
http://www.nettuts.com
Here's the thing, HTML only sites are thing of the past. Most of the websites out there worth their salt have dynamic content and for that you need a server side scripting language like PHP (version 4 and/or 5) (or ASP from Microsoft) and you need to know how to operate database software such as MySQL. PHP is free, open source and a great way to start learning server side scripting and not to mention, it has great documentation at www.php.net and there exist a great number of frameworks for it once you know the basics. Some of these include Cake PHP, Symphony and Code Igniter. Personally I use Code Igniter and I think it's fantastic but that is something you might want to dive into right after learning the basics of PHP 4/5 as well as Object Oriented Programming concepts in PHP. MySQL is also free, has decent documentation and with a software such as PHPMyAdmin, you can easily learn to create, use and manipulate databases fairly well with minimal knowledge of SQL (though full knowledge of SQL would make you more powerful).
If I were you I would start by getting good at the basics such as XHTML and CSS simultaneously. I don't see how you could learn CSS independently from XHTML. Then I would move on to PHP, MySQL and JavaScript. The good thing about JavaScript, however, is that you can learn programming language concepts applicable to PHP and you don't need any server configuration to try it. This does not mean that you can use JavaScript instead of PHP. Great sites use at least both of those technologies.
Now if you want to move to additional cooler stuff you can learn Flash and its scripting language ActionScript but I don't think it is imperative for you to know Flash until you get a feel for PHP and JavaScript.