There are a number of Drupal SEO modules to choose from. Here is a summary of the most popular ones to help with your Drupal search engine optimization.

Module Project Page Version Importance Tutorials
Path http://drupal.org/ handbook/modules/path 4/5/6 must have Path Tutorial
Path Auto http://drupal.org/ project/pathauto 5/6 must have Pathauto Tutorial
Pathauto Settings Tutorial
Page Title http://drupal.org/ project/page_title 5/6 must have
Global Redirect http://drupal.org/ project/globalredirect 4/5/6 must have Global Redirect Tutorial
Path Redirect http://drupal.org/ project/path_redirect 5/6/7 must have
Meta Tags (nodewords) http://drupal.org/ project/nodewords 5/6 must have Meta Tags (nodewords) Tutorial
Meta Tags by Path (nodewords bypath) http://drupal.org/ project/nodewords_bypath 5/6 good to have
Meta Tags Node Type (nodewords nodetype) http://drupal.org/ project/nodewords_nodetype 5/6 optional
XML Sitemap http://drupal.org/ project/xmlsitemap 5/6 good to have
Menu Attributes http://drupal.org/ project/menu_attributes 6 good to have Menu Attributes Nofollow Tutorial
Automatic Node titles http://drupal.org/ project/auto_nodetitle 4/5/6 good to have
Search 404 http://drupal.org/ project/search404 4/5/6 good to have
Links Checker http://drupal.org/ project/linkchecker 5/6 good to have Broken Links Tutorial
SEO Checklist http://drupal.org/ project/seo_checklist 5/6 good to have
SEO Friend http://drupal.org/ project/seo_friend 6 good to have SEO Friend Screenshots
HTML Purifier http://drupal.org/ project/htmlpurifier 5/6 good to have
Google Analytics http://drupal.org/ project/google_analytics 5/6
Service Links http://drupal.org/ project/service_links 5/6 optional Service Links Tutorial
Digg This http://drupal.org/ project/diggthis 5/6 optional
good to have
Nofollow List http://drupal.org/ project/nofollowlist 5/6
SEO Checker http://drupal.org/ project/seo_checker 6
Excerpt http://drupal.org/ project/excerpt 5/6
Alinks http://drupal.org/ project/alinks 5/6
More Like This http://drupal.org/ project/morelikethis 6
Related Content http://drupal.org/ project/relatedcontent 5/6
Glossify Internal Links Auto SEO http://drupal.org/ project/glossify 5/6
Calais http://drupal.org/ project/opencalais 6
Safe HTML http://drupal.org/ project/safehtml 4/5
Urlify http://drupal.org/ project/urlify 4/5
Find URL Alias http://drupal.org/ project/find_path 4/5
Related Links http://drupal.org/ project/relatedlinks 4/5
URL List http://drupal.org/ project/urllist 6
RobotsTxt http://drupal.org/ project/robotstxt 5/6
Page Title by Path http://drupal.org/ project/page_title_bypath 5
Custom Breadcrumbs http://drupal.org/ project/custom_breadcrumbs 5/6
Pathologic http://drupal.org/ project/pathologic 6
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