If you want to add the content query webpart in SharePoint 2010, you might not find it.
For this webpart to be active you have to enable  the SharePoint Server Publishing Infrastructure feature.

• go to the Top Level Site Collection settings.
• click on [Site Collection Features] in the Site Collection Administration Menu (you must be a site collection administrator off course to see this)
• Activate the [SharePoint Server Publishing Infrastructure Feature]

   

You can now add the Content Query Webpart.

note: don’t be disturbed by the blue color