http://code.google.com/chrome/extensions/samples.html

Google Mail Checker
Adds a Google Mail button to the toolbar which displays the number of unread messages in your inbox. You can also click the button to open your inbox.
Included with no charge is a swell animation when the number of unread items changes

Subscribe in Feed Reader
Adds a small icon to the omnibox when a web page contains a feed that can be subscribed to. When you click the icon, present a preview of the feed and the option to subscribe in the web-based reader of your choice.

News Reader
Displays the first 5 items from the 'Google News - top news' RSS feed in a popup. Also shows how a popup can dynamically resize itself to fit additional content.

Other samples
These samples use similar capabilities to the ones above, but to implement different features.
Chromium buildbot monitor: Monitors the Chromium tree status.
Mappy: Easily access a map for the first address on any web page.

Google's own Chrome Extensions Gallery https://chrome.google.com/extensions/ is now available in limited beta release to allow developers to upload their extensions or themes. Extensions or themes developers can now upload their extensions to the Google Chrome gallery, including testing the autoupdate system, and accessing the URL for publishing.

Originally Posted by sarjoor

Google's own Chrome Extensions Gallery https://chrome.google.com/extensions/ is now available in limited beta release to allow developers to upload their extensions or themes. Extensions or themes developers can now upload their extensions to the Google Chrome gallery, including testing the autoupdate system, and accessing the URL for publishing.

I uploaded an extension, it is really simple to use
I hope it will available to users asap!