There are dozens of books, hundreds of websites and thousands of articles on er, websites. I only have time to read a very few.
The single discipline that underpins all the others in the field of website development is website usability. If websites are unusable then why have them?
Practically, a more usable website will be more successful than a less usable one.
The guru of website usability is Jakob Neilsen, the man who raised serious questions about the web's obssession with bells and whistles. He's disliked by most of the eye-candy guys as a result (http://www.useit.com).
This is a fantastic little book by Rachel McAlpine, apparently little known. I found it under 'Dictionaries' in the local bookstore. It contains a wealth of information on how to write for the Internet. She also has her own website (http://www.webpagecontent.com/).
Gerry McGovern (gerrymcgovern.com) is web content guru not afraid to speak his mind and therefore attracts critics which is a good sign. Subscribe to his newsletter, it's always worth a read.
Far too many to list them all but worthy of mention is Nettutsplus (http://net.tutsplus.com/) and Smashing Magazine (http://www.smashingmagazine.com). Net tuts is more techniques and Smashing is more design but there is a lot of overlap. They sell an inexpensive book on web design.
Fancy your hand at HTML? The best site is W3Schools (http://www.w3schools.com).
Colours are very important but most designers do not know how to use them to create a mood. Lots of software and websites but a book can be useful.