It's hard to avoid spying tracking online competition, especially when competitors may make changes or advances quicker than you. The most important aspect of SEO is the ability to stay ahead of competitors but more important is a clear understanding of why you increased ranking results and being able to put solid assessments behind collected competitive data. With that said, our compilation of the best free competitor tools (not to be confused with our Top Free SEO Tools list) focuses on all aspects of your competitors and allows you to understand the competitive landscape to help you succeed. So, here we go:

1. Touch Graph Google by TouchGraph.com

This tool is one of our favorite graphic SEO tools. It gives an amazing view of your site and your competitor's site relationships. TouchGraph.com uses a free Java application to explore the connections between related websites. You can move or toggle the relationships around and separate the "nodes" to make relationships more clear. It comes with several filters to filter out only sites that are similar to one another. You can take a screenshot of your touchgraph and compare it after several months to assess the change of your industry. It also comes in handy to spot potential link partners.

2. Myriad Search by SEOBook.com

This search engine allows you to combine the results of Google, Yahoo, MSN Search and Ask Jeeves in one set of results. This advertising-free search engine also gives you the possibility of assigning greater value to a certain search engine or limit the amount of duplicates per engine. As if that wasn't enough, it also allows you to export everything in CSV. A great tool for viewing competition rankings across multiple search engines.

3. Web CEO free edition by WebCEO.com

For many Web CEO free edition is only an evil scheme of the company trying to make you upgrade ;-). But in all honesty, the free version has enough juice to help you analyze what competitors are doing online and also gives a very powerful ranking and visibility engine. We have tested the paid versions and they lack stability for running an SEO analysis on large sites, but the free version though is great for smaller web sites with less than 1000 pages. Overall, an excellent competitive analysis tool.

4. Top Ten Analysis Tool by WebuildPages.com

Webuildpages has done it again! This tool gives you that quick fix feeling by giving you a detailed comparison of the top 10 results in Google for a particular keyword or phrase. It goes a few stpes further by including "allinanchor," Wayback date," "Backlinks and .edu Backlinks" and more from the ranked sites for that phrase and you compare the results to your site with an easy-to-read table. Tip: To gain insight to your competitors with this tool simply set up a quick monthly reminder to run the report again for a few of your top phrases to get a handle of growth from competing sites.

5. Competition Research by Seotoolset.com

This competition research tool shows the current ranking of your top competitors across all the major search engines. If you combine this information with a little bit of Yahoo Site Explorer then you can really be dangerous in terms of link building or accessing competing site's link building efforts.

6. Google Trends by Google.com

Spoting trends is definetely one of the most important factors for the forward-thinking marketer. In the old days when Google took 60 days to show your page refreshes you didn't have to worry so much about time-sensitive content. Today, even though this tool only would gives you a historic trend (past), by analyzing the patterns, you will be able to understand if it is worth reconsidering a specific market or build upon a new niche or new product or service. In essence, you can couple this tool with a few decent keyword tools to understand why a competitor might be shifting into other business areas.

7. Trend Report by URLTrends.com

This is a very important competitive intelligence tool. It compares Page-Rank, Alexa Rank, Google Backlinks, Yahoo! Backlinks, AllTheWeb Backlinks, Del.icio.us bookmarks, Archived pages, and Page-Rank passed! This tools is worth a second look. It allows you to export your results to Excel (free) or to PDF (with the subscription). Up to 10 Urls may be entered and registered members may check up to 100 URLs depending on their account type.

8. ThumbShots Ranking by ThumbShots.com

We love visual tools because they make things so easy to understand, even from an SEO beginner's perspective. ThumbShots Ranking let's you compare rankings from a search engine to rankings in another search engine. You can calculate the overlapping of links between the two sets of results too. The most important feature is that you can compare one keyword to another keyword in the same search engine (something you can't do in Google or Yahoo! alone). There are also other useful features like comparing a site against the competition for a specific keyword and then by just hovering you can check out a preview snapshot of the sites. Very useful!

9. Page Strength Report by SEOmoz.com

To be able to use this free competitor tool you have to register with SEOmoz. This tool is great in assessing the importance of a webpage. Most newbies and people stuck on PR would say that the best way to know that is by using the PageRank toolbar. But since PR is only useful from a ten thousand foot view, the Page Strength tool is a much better metric of a page's true value.

If you are considering building link prospects for one of your clients, you have to use this tool.

10. Charles Web Debugging Proxy by Karl von Randow

SEO competitor research nowadays is nearly impossible without a good web proxy tool. We've tried some web debugger tools and finally settled on the Charles Web Debugging Tool. You don't necessarily have to pay the $50 to enjoy Charles. It can be used as shareware with certain limitations - but for free. The most important of the limitations is that you can only use it for 30 minutes at a time. For most competitive intelligence SEO you can do restart your browser after the 30 minute period without much hassle. It also comes with a firefox extension that lets you administrate firefox through the web proxy! If you use the tool a lot though, I'm sure the paid version is the way to go.

11. Quantcast's Site Composition Tool

Quantcast can give you statistics on tens of thousands of web sites to understand audience composition such as age, gender or income level of the internet visitor and/or their household. Quantcast analyzes internet log records which includes information such as the page viewed and the IP (internet protocol) address used to access the page. "All of the analysis conducted by the Quantcast system is done using anonymous internet usage information." A decent tool for understanding web site value to advertisers or, for us SEO's, taking a peek under the hood of your competitor's site.

12. Spyfu Competitor Keywords Tool

Spyfu sums it up nicely - "SpyFu lets you see which keywords your competitors are buying and which ones they optimize their site for. Once you understand the competition, you can beat them at their own game or your can exploit their weaknesses." Couldn't have said it better ourself.

13. Microsoft's Adcenter Labs

Even Microsoft gives us some useful competitive tools to help mine some data! The Content Categorization Engine is useful to determine what types of webmasters might be good linking prospects and seeing how search engines interpret your web site. In the right hands, the bevy of tools from Microsoft could help build some solid data to support your company's research with trends from competition.

14. SEOdigger's Keyword/Document Analyzer

SEOdigger.com allows users to analyse which keywords can be used to find a given domain in Google or MSN. It also allows you analyze any site and documents - both your own and your competitors. In the base version (for unregistered users), you can only perform 5 queries per hour. For registered users you can perform unlimited statistics on a compelte domain.

Please list any that we missed below and we'll update the post with ones that help with competitive squashing research. Feel free to also check out our Top 15 SEO tools post made several weeks ago to help you build your SEO tools arsenal.