Boxes and Arrows. A recent entry to the e-zine game with a mission to bring together information architecture and related disciplines. Early material looks promising.
 

EPSSCentral. This site is the second-generation heir to the Electronic Performance-Support Systems legacy. It has lots of useful material which is growing all the time. A subscription to the rich weekly email newsletter is recommended, although it requires a fair degree of filtering.
 

Good Experience. Mark Hurst, long a popular and insightful observer of the on-line scene, focuses on the customer in his site and newsletter.
 

Jakob Nielsen. Jakob is a prolific commentator who needs no introduction to usability professionals. His site is a much used and sometimes abused rich resource of research results and strong opinions.
 

Usability Professionals Association. The UPA is an international organization for practitioners. Their newly launched publication, User Experience, is a promising addition to print resources.
 

Usable Web. This is the link resource on the Web. With over 1400 links, Keith Instone's project is a true treasure trove of on-line resources.
 

User Interface Engineering. This is Jared Spool's home turf. With a much deserved reputation for sound research on Web usability and interaction design, this site houses many useful studies and reports. You may not always agree with the conclusions, but the data is solid.
 

UI Design. A strong human-factors and usability site with a distinct spin. The site is now infrequently updated, but has Interesting interviews with industry leaders, archives of lively discussions, plus a few debatable design patterns from earlier times.
 

Web Pages That Suck. More current but narrower than the Interface Hall of Shame (above), Vincent Flanders's "Daily Sucker" is a fun and and ever-changing resource on bad Web design.
 

Web Word. John Rhodes's venerable resource is a good starting point with a regular email newsletter that is definitely worth getting.