Online:
Lynch and Horton, Web Style Guide.

On reserve:
Lynch and Horton, Web Style Guide.
Nielson, Jacob, Homepage Usability, 50 Websites Deconstructed.
Johnson, Jeff, Web Bloopers: 60 common design mistakes and how to avoid them.
Williams, Robin, Web Design Workshop.

In the Wells library:
Clark, Joe, Building Accessible Websites, 651.8 C59.
Forsythe, Chris, Human Factors and Web Development, 651.8 I598hu.
Schneiderman, Ben, Leonardo's Laptop: Human Needs and the New Technologies, MIT Press 2002.
Spiekermann, Erik and Ginger, Stop Stealing Sheep and Find out How Type Works 655.2S75s.
Tufte, Edward, The Visual Display of Quantitative Information, Graphics Press, 1983.
Tufte, Edward, Envisioning Information, Graphics Press, 1990.
Veen, Jeffrey, The Art and Science of Web Design, 651.8 V41
Williams, Robin, The Non-Designer's Design Book, 655.2 W72.

Other:
My links
Sun's guide to web development.