coderguy

This plugin adds Google Analytics tracking code to all WordPress pages. If multisite/network mode is enabled, this 
tracking code will be the same on all sites, which was the main purpose for authoring it.
It’s very basic.
This plugin includes a settings page that allows users to enable or disable the tracking code, enter their account ID, 
and provide a single domain, which is used for aggregating statistics across multiple sub-domains. For WordPress 
Network installations, this page is located under the Settings menu of the Network administration area. For normal 
WordPress installations, this page is located under the Settings menu of the standard administration area.
I needed this functionality but couldn’t find it elsewhere, so I decided to write a plugin. I’m totally open to improving 
this plugin as well so please contact me with feature requests or bug reports.

Sitewide Google Analytics

This plugin adds Google Analytics tracking code to all WordPress pages. In network/multisite mode, this tracking code will be the same on all sites.

Philipp15b

This plugin allows you to add your code/text to the headers and footers on all the blogs in the blog network and in the backend of all blogs too.
In addition, it is possible to replace the footer bar text in the backend completely.
You can access the settings under Network Admin -> Settings.

Sitewide (Admin) Header/Footer

Change the header/footer of the front- and backend of WordPress Multisite

Sitewide Google Analytics vs Sitewide (Admin) Header/Footer