UPDATE June 2018: Although the tool shown below is no longer available for download, I found it via Wayback machine. I assume it is OK and legal to link to it, seeing as the tool was freeware. Updated links below.
UPDATE: This tool from Wise is regrettably not downloadable anymore. I am not sure if it is OK to distribute it either. It seemed to be a free tool distributed as part of their main Wise Package Studio suite, but I don't think it is open source. I wish they would release it as an open source tool.
The Wise packaging products have been discontinued due to a number of legal issues.
On a related note. To deal with the ridiculously complex command line for msiexec.exe you can use this free msi command line builder tool from Wise: http://www2.wise.com/filelib/WICLB.exe (resurrected from Wayback machine).
Please run the download by virustotal.com for safety.
It allows you to build a command line interactively:
