Website spelling checker – Check your webpages for spelling mistakes.
Backlink velocity checker – See how quickly a domain has been building links (remember, slow and steady!)
SEO moz – Range of SEO tools. Needs breaking out into a SEOMOZ set of tools.
SEO checker – Shows: page title, description, keywords, feeds, PR, sitelinks, backlinks, delicious fans, Alexa ranking.
Xenu link checker – Use Xenu to crawl a website and check for broken links (download and run locally).
Rank checking tools – (£) Needs further research but there are a number of ideas for good tools on here. For example, a tool for combining two KWs into a phrase for Google Adwords
KW density tool – KW density tool for 1, 2 & three work phrases. On-page check.
View a page as a spider would – Send in a spider to a webpage and let it analyse the number of words and number of links from a page.