Designing Web Usability. New Riders, 1999.
Nielsen, Jakob.
This is a great book on usability. It seems like every page has a great picture or visual that will help you think about a better way to design your Web sites to make them useful for your visitors. Definitely one to check out.

The Design of Everyday Things. Currency/Doubleday, 1990.
Norman, Donald A.
A fun book that explores the importance of good feedback in designing systems of all sorts. If you create software or Web sites, Norman's book will change how you approach your craft!

The Non-Designer's Design Book: Design and Typographic Principles for The Visual Novice. Peachpit Press, 1994.
Williams, Robin.
This is a fabulous book. Williams (not the comic!) covers two major issues - design principles & designing with type. But she packs a lot of wisdom & common sense into those two issues. Her acronym for basic design principles alone is worth the price of the book - we guarantee you'll never forget it!

Stop Stealing Sheep and Find Out How Type Works. Macmillan Computer Publishing, 1993.
Spiekermann, Erik & E. M. Ginger.
This book really taught us a lot about typography. Besides covering the history & theory of typography, it also provides plenty of illustrations of hundreds of different typefaces.

Web Design in A Nutshell: A Desktop Quick Reference. O'Reilly, 1998.
Niederst, Jennifer
This is a great book from O'Reilly, & it covers an amazing amount of information. HTML & graphics are covered somewhat in depth, & there are shorter introductions to DHTML, Javascript, CSS, XML, & more. It's a fantastic quick reference to keep on your desk.