Developers can now use new "context menu API" in Google Chrome beta to register menu items for all or a subset of pages. Or to register menu items for specific operations, like right-clicking on an image or movie. If you've lots of extensions installed -- Chrome automatically groups multiple menu items from same extension into a sub-menu.
Also, announced two new experimental APIs: » omnibox API allows to integrate with browser's omnibox. And, you can build custom search support for your favorite website, keyboard macros to automate tasks, or even a chat client right into omnibox » infobars API allows to display infobars across the top of a tab. These infobars are built using normal HTML, so they can be heavily customized and interactive.
For complete list of new extension APIs: docs