The expression tester tool is a standalone application that allows you to easily develop and test expressions. It is like a workbench to quickly try things without having to open a package or mess up the one your currently working on. It is designed to be easily portable, just extract the files and run, but it does require SQL Server Integration Services to be installed on the machine. The download contains both SQL Server 2005 and SQL Server 2008 versions of the tool and control.
You can download this tool at the following link
SSIS Expression Tester
Hope this is useful for all of you.