Search Engine Optimization is a rather complex and never ending process. You have to analyze a lot of things including what keywords people are searching for, the density of those keywords in your sites, how many sites link back to you, how popular your links are and so on. Doing all this manually can be a huge pain.

With that in mind, regardless of whether you're an SEO guru or a beginner, these twenty tools are guaranteed to make your life easier.


Keyword Research

When people - like us - build web sites, they assume they know what keywords people use to get to their sites. For the basic keywords this works but there a lot of untapped keywords that you might be unaware of. Doing the proper research to find out all possible keywords is imperative in this case. The keyword research tools below let you do all that in a jiffy.
Google Search Based Keyword Tool








Google's tool provides keyword ideas and suggestions siphoned directly from Google's search data. This is slightly different from the Adwords Keyword tool in that it suggests keywords not already associated with your Adwords account and provides a lot more information.


Just key in your site and normal keywords and let it provide you with a plethora of new ideas.
WordTracker





An excellent tool, with a paid counterpart, which lets you find out related keywords you might have missed out on so far. It also provides rough estimations of the search volume generated by the keywords.
SEOBook Keyword Suggestions





This tool cross references the keyword you input with multiple search engines to provide suggestions.
Microsoft's Keyword Forecast





This tool predicts search volume and impressions for the keywords you enter into the system. Useful tool when you are about to launch a SEO campaign. Also provides a ton of target demographic data you'd want to take advantage of.
Trellian's Keyword Discovery





Another popular keyword research tool with a paid version available for those who want additional features. Just type in your basic keywords and let it generate a list of top keywords which will work well for you.
Keyword Density


The number of times a keyword occurs in your page's content is extremely important. Be too skimpy and your site won't be counted for that keyword. Go overboard and you'll be penalized for keyword stuffing. The optimum numbers seems to be between 2 to 4 percent and these tools will let you make sure you make this number.
SEOBook Keyword Density Analyzer





Just enter your URL and let the tool do its thing. It shows you which keywords are present most in your content, how many times it occurs and how much place it takes up relative to the other words on the page.
iWebTool Keyword Density Checker





Another tool which looks through your page and creates a tag cloud. If you prefer raw data, it also shows you how many times each keyword occurs on your page.
Webconfs Keyword Cloud





Webconfs' tool produces a keyword cloud for easy perusal. Just like with other tools it also produces a listing of which keyword occurs the most and its density.
Search Engine Rank Checkers
Link Vendor's Page Rank Checker





This Page Rank checker lets you find out your Page Rank at individual Google data centers.
PageRank Tool





This tools lets you find out your page rank quickly with minimal fuss.
Self SEO Rank Checker





You can find out your PageRank and Alexa rating along with a bunch of other useful info using this tool.
Link Popularity


A major part of SEO is getting linked. The number of backlinks you are getting is a fair approximation of how well your site is doing and makes tracking this statistic an important affair. Using these tools, you can find out who links to you, which pages are linked the most and a lot of other data.
WebMaster Toolkit Link Popularity Checker





Just enter the URL in question and it'll show you how many pages popular search engines link to through their search engine result pages.
SEOCentro Link Popularity Check Tool





Lets you know how many incoming links you have and breaks it down to individual search engines. Also provides an interesting table of sites with differing numbers of incoming links for reference.
LinkVendor's Link Popularity Tool





An excellent tool which provides a plethora of information including how many web sites link to you, how many individual linkbacks you get, your PageRank, your Alexa rank and so much more.
Site Analytics


Monitoring your site's traffic, page views and visitor behavior is extremely important once you've finished the initial SEO to make sure your plan is sound. Use these tools to track down your site's statistics.
Google Analytics





Google Analytics provides an extremely slick summary of your data. Use it to check which pages get linked to the most, how much time people spend on your site, what percentage of visitors are new and a lot more.
Compete





Just like Google Analytics, this tool presents an extremely pleasing way to monitor your site's well being. As a fun feature, it lets you compare the stats of up to 5 different sites.
Mint





If you don't mind a paid solution, Mint is a top-notch analytics suite which a lot of developers swear by. It features a beautiful interface to present all the data.
Crawl tests


Understanding how your pages look to spiders (heh) is important while optimizing for them. This lets us strip out all the visual elements and see the page as a crawler would see. Such a test helps you understand how accessible a page is to a crawler and lets you weed out potential issues before full deployment. These 3 tools let you do just that.
SEOTools Spider Test





This tool not only lets you see how your page looks to spiders but also returns a lot of useful information including the number of words in the page, the keyword density and pages you link to.
iWebTool Spider View





If you are just looking to find a tool to simulate a spider without any extra frills, this is the tool for you. Crawls through your site and lets you see how it looks to a bot.
WebConfs' Spider Simulator





WebConfs' Spider Simulator simulates a spider crawling through your site. Shows you how a page looks to a spider and also nets you the list of sites you link to, the meta description and meta keyword.
Conclusion


I hope this list made it easier for you optimize your web applications for search engines. With the internet being a big place, I am sure I've missed a ton of equally useful SEO tools. Let us know about these hidden gems in the comments. Thanks for reading!