The OpenJDK Wiki has a new home at wikis.oracle.com. It should look and feel very similar to what you've been used to as this uses the same underlying Confluence software. The older sun.com-hosted wiki is still accessible but it now redirects to the newer instance.
The most important change is probably that the Wiki is now Oracle SSO-protected. That means that you'll need an Oracle.com account to make edits. In other words, the old wikis.sun.com account won't work for that.
In addition, you need to be an editor for the Wiki in question.
So if you'd like to edit the OpenJDK Wiki, the ProjectCoin Wiki, the HotSpotInternal Wiki, and the MLVM Wiki, please send an e-mail to the web-discuss mailing list at openjdk.java.net with your Oracle SSO Username and the name of the OpenJDK-related Wiki you'd like to edit, and your request will be processed by one of the wiki owners. (If you haven’t already subscribed to that list then please do so first, otherwise your message will be discarded as spam.)