When using SQL Server Integration Services, I like to keep things flexible and therefore I keep any hard coded names in variables. This means using the expression builder quite a lot, but the problem is the font size for the actual Expression is way too small, especially when writing code.
I find myself copying and pasting between SSIS and Notepad++ a lot, There must be a way to adjust the font size but I haven't been able to find it.
Another option is to grab BIDSHelper. It's a free addin to visual studio. When editing variables, you have a new pop up window to handle expressions. It gives you a bit more real estate to work with. It unfortunately won't help with the derived column transformations. I find that if my expressions scroll off the pane, that's usually an indicator it's time to push the logic into a script transformation.
use this 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.
Instead of using a stand-alone application, try BiXpress, Community Edition. It integrates itself into the Visual Studio (or BIDS) and is free: http://pragmaticworks.com/Portals/0/ProductInstallers/bixpress_x86_x64_community.msi
It has more features than you were looking for.
