Competitive Analysis- Tools & Techniques

Understanding your competitors -- their strategy, their tactics, their level of success, etc. -- is crucial to the success of your SEO initiatives. I'm not just talking about your traditional competitors, I'm referring to the other sites occupying spots in the SERPs (search engine results pages) for keywords that you are targeting.
Many free competitive analysis tools are out there, but you have to know where to look for them. One of my favorite SEO blogs (Stuntdubl) offers a veritable Home Depot of such tools, at Mr. Ploppy's Monday Tool List.
It's a bit like walking into a DIY store and being faced with an overwhelming array of options. What is the right tool for the job?
Here's a sampling of some of the SEO tools that I use for competitive analysis and what I specifically use them for:

• URL Checker, Product Page Checker -- to check saturation (# of pages indexed)
• PageRank Lookup, PageRank Search, Webmaster Eyes, SEO-Links -- to run bulk checks of PageRank scores, to analyze PageRank flow
• Neat-o -- to review anchor text of inbound links
• Link Checker, Yahoo Site Explorer -- to check link popularity and review inbound links
• Alexa -- to check Alexa Rank and review traffic trends on someone's site
• What's That Site Running -- to determine what server software a site is running
• Check Server Headers -- to see what type of redirect (301 or 302) is being used; to see if a 404 is being served when it's supposed to be, etc.
• Keyword Ranking Tool -- to track positions in the SERPs