Apple has released a new version update for iTunes today that brings the application up to version 8.1.1.
iTunes 8.1.1 adds support for renting HD movies and provides a number of bug fixes, including addressing issues with VoiceOver and syncing with iPhone or iPod touch.
iTunes 8.1 was released in early March and added a number of new features.
The update should be available in your Mac OS X Software Update.