Like it or not you've got to do SEO and keep it on your radar at all times. Here is a list of the best free tools related to Search Engine Optimization. These tools try to bring in all the aspects of the complicated world of SEO and make it easy for you to get a grasp on how friendly your domain name is to search engines like Google and Yahoo, and how popular it is within its related topics.

The Main Players are:

Alexa has a nice charting system. You can see your Reach, Rank and Pageviews charts and filter using date ranges and compare to other domains as well. QuantCast gives you Traffic overview, US Demographics, Brand & Site Affinities, Similar Audience, Top Subdomains and traffic charts.

Here are some of the best tools to check your PageRank and more:

TagURLs is a web analytics tool combining the top 500,000 U.S. websites with their topic tags, using data from del.icio.us and QuantCast. Use it to discover the most trafficked sites for any topic of interest, such as "videos" or "education", or by url, such seifi.org.

SEO Keys is a nice tool to search your domain for sites that link to you and their respective PageRank

Compete shows you a snapshop of your domain with a People Count chart and Top Keywords.

UrlTrends gives a trend report for your domain, that includes PageRank and Alex Rank, Incoming Google Links, Incoming Yahoo Links, Incoming MSN Links, Incoming Alexa Links and more.

Submit Express gives a nice table of your keywords, urls and a good analysis of your meta tags.

SEOmoz displays its own Page Strength and shows you details on how it calculates that score.

URL Investigator shows basic information such as Google Pagerank, Alexa Traffic Rank, WhoIs and Link Check data.

popuri is a simple Ajaxy tool that gives you the Google, Alexa and Quantcast Ranks, Google BackLinks, Yahoo BackLinks, Live Search BackLinks, Technorati Links, del.icio.us Bookmarks, Bloglines subscribers and more.

Statsaholic shows charts from Alexa and Quantcast for up to 3 domains.

WebConfs is another powerful and tool with lots of SEO checking utilities, such as Keyword Density Checker, Keyword Suggestions and more.