Finding solid textbooks on web design is always a challenge. There are plenty of expensive, thick reference books for developers, but textbooks can be a bit dodgy. Besides, as my regular readers know, I'm incredibly cheap. I have trouble spending money on anything printed to teach computer technology when the technology itself is so often outdated by the second semester.
The Web, on the other hand, tends to avoid these pitfalls: the content is not only free, but also stands a much better chance of being up to date. Thus, I'm always on the lookout for great instructional sites. An old standby for me is Tizag; I know the name is cheesy and the content isn't flawless, but it's well-organized and covers everything from straight HTML to ASP. Students have found it to be a really good reference, even as they become more adept, but it's quite easy to follow for the beginner.
Once students really start thinking about scripting, though, and get past the basics, a better treatment of PHP is really necessary. PHP has matured from a tool for geeks to add some funk to their pages to a de facto standard for dynamic page development. It's fairly straight-forward, but new students would do well to look at the site I stumbled upon via Digg yesterday: Devzone has a really outstanding set of tutorials on PHP, running from the extremely basic to the fairly advanced. Bookmark it for your students and do us all a favor and submit your favorite sites via Talk Back below.