Assuming you have Active Directory in production, group policy software installation policy and MSI files (either off-the-shelf or custom-built) are a cheap way to do automated installs of applications onto computers. Group policy is also a great way to configure the computer and user environment with consistent settings (using security options, administrative templates, startup scripts, mainly).
There are a boatload of tools to build MSI files out there (since some software manufacturers still don't understand that using the OS built-in installer is a good thing... >sigh<). I'm partial to the Windows Installer XML toolset (WiX-- see http://wix.sourceforge.net/) because it's very easy to version the WiX source-code files in a version control repository, create and manipulate them with scripts, etc.