I frequently need to re-image my machines, as a result, I need to install a bunch of apps (skype, paint.net quick time, picasa,etc). Every time I need to do this I forget that last time i found an app that solves this problem.
The app is called ninite, and it creates an on the fly downloader/installer for all the apps you want to install. Give it a try the next time you need to reimage a machine.
Hopefully, this will help me remember what I'm doing for next time.