http://www.seomoz.org/tools 
Free and Paid
Linkscape: An inlink tool that finds competitive details of your competitors like anchor text, keywords, links and other factors responsible for their top rankings.
Crawl Test: A diagnostic tool for search engine crawler issues which checks for response codes, cache dates, number of internal links on each page etc.
Trifecta: Estimates the popularity and importance of page, blog or a domain. Find which pages or areas of your website is weak and who is strong in your area.
Strongest Pages: Know which pages from your website stand out to be in better SEO compliance and which not.
Check Indexed Pages: Check the status of your web pages included in top 3 search engine Google, Yahoo and MSN.
Keyword Difficulty: Analyzes the current competition for targeted keywords and determines the difficulty level.
Backlinks Analysis: Measure the amount of links pointing to your website.
Check PageRank: Know the google page rank of your parrticular web page.
Popular Searches: Provides popular search terms being used at different sources over the web.
Term Target: Analyzer various factors on a page to find how well a particular page is targeted via keyword.
Term Extractor: Analyzes the content of a page and extracts the terms that appear to be targeted at search engines.
Rank Tracker: Track and monitor your search engine rankings for Google, Yahoo!, Live and more.
GeoTargeting Detection: Find out how well your site is targeted towards country specific search engines.
Site Intelligence Service API: Seomoz API provides an interface to developer and programmers to use tools and data which can extract information and use in their own applications.
Firefox Toolbar: The Seomoz linkscape feature can be directly utilized via this add on firefox toolbar. Besides this you can also get easy access to mozrank and moztrust instantly.
SEOmoz Labs: A place to fine out the ongoing research and developmental tools at Seomoz.
Seo Toolbox: A collection of commonly used search engine optimization utilities.
Juicy link finder: Find links that have trust authority like old domains with high PageRank, which ranks well for the keywords.