Here are some free online SEO tools that will help you stay on top of your SEO efforts:
1. Rank Checker by Seobook.com
This tool is a quick and easy way to determine which of your keywords are ranking for your site in all of the major search engines. I use this tool to find my keywords that aren’t in the top 5 pages of Google/Yahoo!/Bing. This isn’t always exactly accurate, so do a manual search if possible. We have also found that if you use this tool too much, Google will penalize you because it thinks you are a spammer. So use the tool wisely, and it will benefit you.
2. SEO for Firefox (add-on)
This tool will give you PageRank, cache date, domain age, backlinks in Yahoo, number of .edu links, the number of cached pages, and a number of other stats. This is perfect to analyze and evaluate your competition.
3. Firebug (Firefox add-on)
4. Google Analytics
Google Analytics helps you analyze your visitors. It shows you the number of returning visitors, the number of absolute unique visitors, where those visitors are located on the map, which pages were viewed, and how the visitors got to your site. This will help you analyze who to target and whether your SEO efforts are paying off!
5. SEO Analyzer by: Sitening.com
This is a great starter tool. SEO Analyzer will help you asses how much SEO work a website will need.