Yale Web Style Guide - already a classic but still update. Free from the University of Yale, USA. Also available as a book.
Creating Killer Web Sites by David Siegel (book)- controversial... contagious ? In 1998 the author published a second edition, taking into account the changes occurred since 1995, date of the first edition.
Great Web Architecture by Clay Andres (book, 1999) - a thorough and carefully written book. Its arguments are grounded by examples reviewed in detail and interviews with leading web designers. I read the french translation "Votre atelier Architecture Web".
Jakob Nielsen (on line column, twice a week). Opinions, advice and commentaries on web design and future trends on the Internet. Co-founder of Nielsen-Norman Group
askTOG:Bruce Tognazzini, author of this column, is a collaborator of Jakob Nielsen at Nielsen-Norman Group. His column emphasises the user interfaces, which complements Nielsen's views.
Shorewalker.com by David Walker - Comments and reviews about Web design. Includes summaries about tests and trials, technical reports, conference papers, etc with emphasis on Australian issues.
Web review - An online archive of papers and manuals by different authors. Spans different areas in a technical and objective approach. Features standards reference guides and tables of browser compliance to the different standards.