Macromedia Flex Builder 1.5
 

Flex Builder lets designers and developers build Flex applications more productively. Designers can quickly build application interfaces, laying out compelling Flex user interfaces quickly and easily, and connecting them to back-end data sources. Developers can code and debug Flex applications productively using code hinting and debugging tools. With Flex Builder, you can include everyone on your team to produce more effective Flex Rich Internet Applications.

Pricing starts at $12,000 USD

http://www.macromedia.com/software/flex/flexbuilder/