Examine Installer Packages Using Quick Look
Suspicious Package is a plugin for the Quick Look feature of OS X. It allows you to preview the contents of a standard Apple installer package without launching the Installer. Just select the icon in the Finder and select Quick Look:
You can click on individual folder names to see their contents, or click the Show Contents button to see all content at once. Suspicious Package also alerts you to packages that require an administrator password, or that require you restart your machine after installation.