A few years ago I got this book on design patterns for web design - graphics, html and visuals. It was a really interesting book, it collected a few years worth of web design best practices in a single place, covering everything from navigation (tabs, breadcrumbs, drill-down, etc) to shopping carts. It talked about the popular-thus-familiar ways the best patterns worked, and some pitfalls to avoid when using them. It also showed a lot of screen shots of the design in action. I hadn't seen any other book like it, so I ate it up. I highly recommend it, I believe there is a newer edition out now.
Today I discovered that the always interesting Yahoo Developer Network has a Design Patterns section, and it seems to have a lot of cutting edge patterns. I'm very pleased to see design patterns for web design becoming more mainstream - it's kind of a sign of the industry maturing.