There are lots of search engine optimization tools available, so let's highlight some free SEO tools as well as some inexpensive ones.

• Google Analytics - Plugging in free Google Analytics tool into your site is good for SEO because there are
• Google AdSense - If you put Google AdSense ads on your website, you will be provided with traffic and click (conversion) reports. You can setup "channels" so that many ad campaigns (across different domains or across the same domain) can be tracked separately. There are advanced reports for seeing traffic/clicks per day/month/year/etc as well as for "ad units" (see right side block) vs "link units" (see below this content).
• Google Toolbar - The Google toolbar will show you the pagerank of a web page, access to the cached version of the page (if available), and a list of links that go to the web page (backward links). Note that the backward links may not be accurate (I remember reading a long time ago that Yahoo's backward link feature was more accurate.)
• SEO Book Toolbar - Nifty Firefox toolbar that shows all sorts of stats for the web page you are viewing including number of external links, internal links, pagerank, estimate traffic, social bookmarking stats, rank checker, and more.
• WordTracker - WordTracker has a free keyword suggestion tool that will show the top 100 keyword phrases with the given keyword in it. It also free week-long trial of their more extensive online SEO tools. If you want to do keyword research, this is a good resource. After the free trial, you'll pay around US$60/month or US$350/year. I used this tool extensively in the past for finding keyword combinations with low competition but decent traffic (good KEI score).