I get asked fairly frequently what resources I used to learn what I know. Truth is I've been building websites as a hobby since '03 and frankly the learning curve has gotten easier with browsers now following a general standard (Well Internet Explorer still likes to be "special" but it's better than it used to be).
Here are some resources that I used and sometimes still use for reference:
http://good-tutorials.com - Just a general list of Tutorials, they cover everything from HTML to Flash, it's a good place to learn a couple of new techniques or to gather ideas. The best part about this site is that it actually links to other websites with even more tutorials really this is a very valuable resource.
http://www.w3schools.com/ - I still use this site when I need to look up CSS syntax. It's really best as a reference but they give you examples of code and how it will come out.
http://www.php.net/ - If you're interested in learning PHP you can google a few basics or use Good Tutorials to get you going but when it comes to looking up functions or syntax, or even with help with a problem you can't beat PHP.net.
http://dev.mysql.com/ - Again if you're interested in learning MySQL you can google some Tutorials or use "Good Tutorials" to look up some "Getting Started" guides but when it comes to syntax and function look ups, can't beat the MySQL Developer's center.
If you're interested in picking up any "How To" books I generally discourage it because 99% of the information they will provide you can look up on the internet for free. One of the most rewarding experiences as a developer is picking up a book and skimming over it real quick only to realize you already know everything in that book.
If you have any questions please feel free to ask.
Disclaimer: This is not a promotion or an advertisement. Please do not ask questions about what you should charge people or what is a fair price to ask as this is technically illegal. These links and my comments in this post and all of my posts in this thread are for educational purposes ONLY.
I know there are other developers on this forum and I encourage them to post any differing resources they have.