Working with Joomla SEO on a daily basis, I've been through every SEO tool available. There's only one that has proved to be indispensible - the Joomla Search Engine Optimisation Patch from Joomlatwork.com.

What does it allow you to do?

• Have complete control over page metatitles
• Control whether Google takes a snippet from your page for the results page
  
• Easily add "follow" or "nofollow" links to individual pages
• Add custom meta fields
  
• Disable the Joomla meta generator tag

All of these are key factors in giving your site a ranking boost. JPromoter from JoomlaEquipment.com does similar things. The disadvantage there is that you need to run a scan every time you add new content, although it has a major benefit in that unlike Joomlatwork, you don't need to modify core files.