A developer-only release of Silverlight 3 Beta has been released.
Check out Welcome to Silverlight 3 Beta. This page gives you links to the Beta runtime, tools, documentation, samples, and summary of what's new in Silverlight 3 Beta.
Also, I'm copying down the "What's new in Silverlight 3 Beta" from that page here so that I can add links to new MSDN topics/API that correspond to some of the new features. See Welcome to Silverlight 3 Beta for the complete list including what's new for Blend 3.
Support for Higher Quality Video & Audio. With support for native H.264/Advanced Audio Coding (AAC) Audio, live and on-demand IIS7 Smooth Streaming, full HD (720p+) playback, and an extensible decoder pipeline, Silverlight 3 brings rich, full-screen, stutter-free media experiences to the desktop. New and enhanced media features in Silverlight 3 include:
Empowering Richer Experiences. Silverlight 3 contains new 3D graphics, animation features, hardware accelerated effects and text improvements that enable designers and developers to create next generation Web visuals. Additional features include:
Improving Rich Internet Application Productivity. New features include:
Advanced Accessibility Features. Silverlight 3 is the first browser plug-in to provide access to all system colors, allowing partially-sighted people to make changes such as high contrast color schemes for ease of readability by using familiar operating system controls.
Out-of-Browser Support. The new out-of-browser experience in Silverlight 3 enables users to place their favorite Silverlight applications directly onto their PC and Mac, with links on the desktop and start menu—all without the need to download an additional runtime or browser plug-in. Further, the new experience enables Silverlight applications to work whether the computer is connected to the Internet or not—a radical improvement to the traditional Web experience. Features include: