SharePoint Infuser by Muhimbi
SharePoint Infuser allows custom content, any content, to be inserted automatically on every page in a SharePoint site collection. Infuser is a completely free product, you can download it and use it in your production environment free of charge with no strings attached.
In essence Infuser is used in a similar way to the many existing Content Editor Web Part (CEWP) ‘hacks’ published on the Internet. The main difference is that the CEWP must be added manually to every page in a site - which doesn’t scale – whereas Infuser inserts the code automatically on every page in the Site Collection.
I am amazed with this software and how cool it is! Especially that it's FREE!