I know HTML and Javascript, but was wondering what languages I should know to build more interactive websites. By this I mean I want to update a site automatically every so often without having to load the files myself. What language gives you the ability to do this type of stuff the best?
You want to make a CMS- content management system. Drupal is my favorite framework for this. Check it out.
To make interactive websites js + html (+css for styling) is enough. (php + mysql is the easiest for database & backends)
But for easy coding you should use libraries such as JQuery, Mootools or Prototype (these are the 3 I have used so far, there are more, you can find some more at http://code.google.com/apis/libraries/).
Some of the most popular content management systems, like Drupal, Joomla, and Wordpress, are built with PHP. It's pretty easy to learn the basics, and the syntax is somewhat similar to JavaScript. You'll also need to learn how to use a database system; MySQL is very common. Both of these technologies are available on almost all web hosts.
Other common server-side languages are Python and Ruby, which are commonly used through the Django and Rails frameworks, respectively. As powerful as they are, they will probably take a little more work to set up depending on your hosting provider.
If you want to roll your own system, then I'd recommend taking a look at CodeIgniter. It's a powerful PHP framework that isn't too hard to learn.