Hi
In last six month I have tried to optimize my site for the Search engines. When doing so I am constantly looking at some of the sites/tools to know the position of my site in regards. These are publicly available free tools and shows statistics for websites. Here is a list of things that people might be interested, in context of there site.
Technical data of a site
IP Address - by DomainTools Search
Other Sites on an IP Address - by IP Query at Live.com
Name Server - by DomainTools Search
W3C Validation for the site page - by W3C Markup Validator
CSS Validation - by W3C CSS Validator
Statistics on the popularity of the Site
Alexa Rank - by Alexa
Alexa Reach - by Alexa
Alexa Page Views Estimate - by Alexa
Google Trends Data - by Google Trends (only available for High traffic site)
Ranking.com Rank - by Ranking.com
Netcraft Ranking - by Netcraft
Bloglines Subscribers - by Bloglines Feed Search
Data on Search Engine Indexing
Google's Indexed Pages - by Google site: command
Yahoo! Pages Indexed - by Yahoo! Site Explorer
MSN Pages Indexed - by Live.com site: command
Ask.com Pages Indexed - by Ask
Gigablast Pages Indexed - by Gigablast Advanced Search
Data about the site linking.
Yahoo! Link Data - by Yahoo! Site Explorer
echnorati Link Data - by Technorati
MSN Link Data - by Live.com link command
Google Link Data - by Google link command (This data is always inaccurate)
Google PageRank - by RankAlert
If you have any more links to add to this feel free to share.
Hope this helps
Thanks
Vikram