This document was created by a set of user interface designers, usability specialists, and visual designers, to outline a usable web application look and feel that can be followed consistently throughout a product line. We created it originally for use within Sun Microsystems, to be used for the web applications built here. However, we would like to share these guidelines with anyone else who may benefit from them for creating their own web applications. While some of the guidelines refer to Sun-specific elements and contexts, we are confident that you, the reader, will be able to interpret how they can be reapplied to your applications. We hope you find these guidelines valuable, and wish you success in creating your own powerful and highly usable web applications, building on these usability-tested and carefully designed guidelines.
see here for the full guide