Some good answers so far...
First, regarding books. While the suggestion of avoiding "dumbed downed" books has some merit it is worth noting the distinction between books that are primarily used for reference and books that are more about theory. I haven't fund much use for "reference" books so much as usually the same material can be found online and kept more up to date. However, theory books on algorithms and software design can provide a good background on how, in general, to write good code. One of the best ways to learn how to write good code is to learn by example, and one of the best ways to do that is to surround yourself by others that write good code. Find an area of interest, then look for a good community open source project, then join their mailing lists, and become involved with the community. While you probably wouldn't be making too many contributions to the Drupal core, there is a lot that can be learned by following the Drupal development community to observe coding best practices, software design and patterns that experienced coders use. Drupal is just an example here. IMHO, a good software application/system begins with a good architecture, and a good architecture makes it much easier to write good code.
