MSN : http://webmaster.live.com
Google : http://www.google.com/webmasters/
Yahoo : http://siteexplorer.search.yahoo.com/
Ask : http://submissions.ask.com/ping?sitemap=http://www.yourdomain.com/sitemap.xml This is for submitting sitemap.xml only.

Whois service : http://whois.domaintools.com

social meters(http://www.socialmeter.com/) check links in major social folksonomy sites such as del.ios.us
Quark base(http://www.quarkbase.com/)
Google analytics(http://www.google.com/analytics/)
Technorati's blogg info(http://technorati.com/blogging/)
Cube stat(http://www.cubestat.com/) - v
DNS scoop(http://www.dnscoop.com/) - negative for foregin (outside US) sites.

For web analysis and optimization:
For the reference: