Some good resources to start:
- Mozilla Developer Network: For HTML, CSS, Javascript, & DOM.
- Dive into HTML5: For learning all about HTML5
- JSfiddle: For fiddling around without having to build a whole page every time.
- HTML Validator: For making sure the HTML you write is valid.
- CSS3 Preview: Run-down of some of the new features of CSS3.
- Official HTML5 spec: For when you need all the detail straight from the source.
- jQuery: Arguably the best framework for making writing javascript for websites easier.
- A List Apart: "For people who make websites". Definitely not for starting out, but good to read regularly.
- Firebug: If you're using Firefox, this is a must-have.
- Developer Tools: built in to Chrome & Safari (essentially firebug for webkit)
Also, do not use W3 Schools. Please see W3 Fools for a long list of reasons why. W3 Schools will often come up at the top of search results, but please resist the temptation to use it.
