The WebAIM Color Contrast Checker is a great tool. Using it should be listed as a must do early in the planning and design of any web site. Within seconds you know if your color choices will pass or fail color contrast accessibility standards.
Peachpit’s Author Interview program with Jeffrey Zeldman about the latest edition of Designing with Web Standards is worth your time. It’s about 40 minutes long.
Twitter is rolling out a retweet function, and it needs some explaining. Demo Girl explains it, and so does Evan Williams.