Free Online SEO Tools

Submit a Website to Search Engines:
Google url Submission
Yahoo url submission
Bing url Submission

Free Automatic Search Engine Submission
Quickly and easily submit your site to many search engines at the same time with just one click.

Meta-tags explained
A good source for understanding the function and proper format of meta-tags. 

Free Meta-tags Generator
Meta Tags are essential to help search engines catagorize websites correctly, and are the basis for proper SEO (Search Engine Optimization).  This is an SEO must and is a great tool to help write and format your tags correctly.

W3C HTML Validator
This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc. If you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets, MobileOK content, or to find broken links, there are other validators and tools available.

XML Sitemaps
This site describes the XML schema for the Sitemap protocol.

Robot.txt
The robot exclusion standard complements Sitemaps, a robot inclusion standard for websites.
  
Google Webmaster Tools
A great webmaster resources that helps you with your crawling and indexing questions, that can enhance and increase traffic to your site.

Mon.itor.us
A Free website Monitoring tool that allows to track performance, availability and website traffic.

DMOZ
Open Directory Project