Today I wanna give a short insight on canonicals. A canonical is a (fairly new) SEO item in the head section of a HTML document, which contains the parent URL. Let's say you have a page which contains a sortable list whose URL is www.chip.de/sortable-list. Besides AJAX-sorting you also have sorting with URLs like www.chip.de/sortable-list/order/price/dir/desc, which reloads the page showing the sortable list ordered by the price descending. Usually you either 2 would have pages in the Google index with the almost the same content or 1 page since you put noindex,nofollow in one of them. This is where canonical comes into play:
First off you leave the noindex, nofollow in the page with the sorted list. Second you put a canonical into the HTML head section telling search engines where it can find the original list!
<link rel="canonical" href="/sortable-list">
That way the sorted list URL will not only not be in the Google index but the original URL gets more "attention".
The latest Firefox versions already show if a canonical is defined:
P.S. It does no harm to put the canonical tag in the original page itself.