I am looking an installer creator for long time. I found Nullsoft Installer, that is free and opensource. I have tried wix installer before, that is too complex to use. Although nullsoft has not a GUI as well, there are a number of scripts and a number of plug-ins provided. I have built some installers without any toubles. However, please run as Administrator in Windows Vista, unless you will get an "Can't open output file" error!

Download at:
http://nsis.sourceforge.net/Download