PageRank Search Tool Tool to search Google using any keyword(s) you wish. It will then return, in order of Google relevance, the sites associated with those keywords. Each result displays a graphical bar with the PageRank of that particular site.

Keyword Difficulty & Top 10 Competition Analysis Tool Measures the difficulty of a keyword phrase including measuring the strength of the top 10 results for the phrase @ Google

Site Analyzer Tool Compares a given site with up to ten other sites and displays competitive search ranking information across multiple search engines.

Link Analyzer Tool Checks multiple search engines for deep links to the target site.

Keyword Density Analyzer Examines elements of your web page for keyword density on selected keywords.

Overture Keyword Tool Reports keyword results from Overture and Wordtracker, enhanced with search figures from the previous month, statistics for average searches per hour, day, week, projected figures for the next 12 months etc.

Overture Keyword Selector Tool Lets you view how many times a keyword and related keywords have been searched for on Overture in the previous month.

Google Autocomplete Suggestion Tool Generates sub-terms of keywords, along with rankings, from the Google Suggest tool

Keyword and Backlink Tracker Tracks your backlinks and results on specific keywords for multiple sites over time. Requires (free) registration and (also free) Google API key.

Google API Key Registration form for Google Developers. Registration (easy and free) gets you a Google API key, which is required to use several of the web-based SEO tools.