Source -As Microsoft’s alternative to Adobe Flash evolves, so does the development tools designed to assist developers in creating content for Silverlight. At MIX10, concomitantly with the unveiling of Silverlight 4 Release Candidate, the Redmond company also announced the availability of the first Beta for Expression Blend 4. At MIX10, the software giant emphasized the fact that Expression Blend 4 was designed to enable developers to build applications for the next version of Silverlight, which is scheduled to be released to web in April 2010.
Expression Blend 4 Beta Released - And available for download - Softpedia