Based on Google search results of course, this Google tool shows you relevant keyword ideas and their Adwords competition for your website.   Related posts: Get New Keyword Ideas Stats On PPC Ads Monthly Keyword Search Volume

A basic tool to see how difficult it will be to rank high for a given keyword or keyword phrase in the SERPs. SEOchat doesn’t give specific info about how they arrive at the result (anything else besides number of searches and SERPs?), but a few test searches turned out

This tool at SEOworkerss gives you an overview of basic aspects of your page, like meta tags; keyword density; page load time; title meta tag relevancy to page content; robots.txt file and more.   Related posts: Free SEO Analysis Tool Meta Tag & Keyword Analyzer How Hard Is It To

Are the right keywords prominent on your page? Find out with the keyword analyzer at Ranks.nl. It also lets you compare the results to your competition and shows meta, outgoing links and more.   Related posts: Keyword Density Checker Meta Tag & Keyword Analyzer Get New Keyword Ideas

Spacky picks up searches from Google, Yahoo and MSN and displays them side-by-side. Works pretty well, but doesn’t pick up lower search volume keywords and phrases.   Related posts: Keyword Trends Google Keyword Search Tool Keyword Suggestions Tool

View, classify, and download comprehensive data about internal and external links to your site with Google’s WebmasterTools. You can also see how visitors get to your site.   Related posts: Link Popularity Checker Analyze Backlinks Instantly External Link WordPress Plugin

Validate and fix your feed at FeedValidator. Works for Atom, RSS and KML.   Related posts: Create Custom RSS Mashups Email Your Feed Info On Your Feed, Cache, Search And Links