The Test Realm for the 1.8 Patch is now live. Here is the information from Blizzard:

The Public Test Realms are live! Players can now experience, and help us test, all the changes and additions coming in patch 1.8, including four outdoor raid dragons, completely revamped Silithus, Druid talent improvements, and many other exciting features. Click Here to view the patch 1.8 test-realm patch notes to learn more!

Players can participate in the test realms by creating a character or by copying their characters from existing realms to the test realms. Those who have previously copied their characters to the test realms will need to do so again, as all previous characters have been removed from the previous test realms. To copy your character and to download the test client, visit our Test Realm Character Copy page. During the first week of testing, only players who created their accounts before August 2 will be able to login to the public test realms. Also, players will not be able to log in to the public test realms if they have changed their password since August 16. All players will be able to access the test realms after next week's maintenance.

Please be aware that the test realms are there to allow us to test major content patches before the patch goes public. Therefore, some changes may be introduced to the public test realms before a patch goes live, and some changes may be introduced to the patch after the test realms have closed. To read more about the test realms, please review the Test Realm FAQ. We truly appreciate our players taking the time to help us test the latest changes to the game; thank you all!