New Canonical Link Tag - Duplicate Content
Google, Yahoo! and MSN have come to a consensus on a new tag that can steer the engines straight on duplicate content.
The new tag is the <link> tag. It tells search engines which URL is the correct one to index.
Similar to meta data tags - the link tag goes in the <head> section of the page. Here is an example:
<link rel="canonical" href="http://www.lunawebs.com/blog" />
You can see more details on the canonical link tag here.