I'm pleased to report that the public beta of Expression Blend, formerly known as "Sparkle" and "Expression Interactive Designer," is posted:

http://www.microsoft.com/downloads/details.aspx?FamilyId=EE6B5E7E-E1E8-4787-BF18-03C2E938A397&displaylang=en

 I've been playing with it for the last several days, and it's pretty sleek. Enjoy!