Adobe has released Flash Builder 4 (http://www.adobe.com/products/flashbuilder), a new suite of web development tools that replaces Flex Builder. It costs US$699; upgrades from previous versions of Flex Builder are $299.
Adobe Flash Builder 4 is designed to help software developers rapidly develop cross-platform rich Internet applications (RIAs) and content using the open source Flex framework. It includes support for intelligent coding, debugging, and visual design and features powerful testing tools that speed up development and lead to higher performing application.
Adobe Flash Builder 4 is available for Mac OS X and Windows. A demo is available for download.