Apple has released iTunes 7.2, as well as QuickTime Security Update 7.1.6, for Mac OS X and Windows. The iTunes update adds the ability to preview and purchase DRM-free tracks from participating labels on the iTunes Store, a much-anticipated feature that is now being referred to as iTunes Plus.
The QuickTime Security Update is recommended for all users and improves security (no specific issues are mentioned in Apple's description).
The updates are available now for download through Apple's Software Update utility, as well as Apple's web site. Software Update may require you to install the QuickTime update before it will detect the iTunes update.