Afterburner is the fastest Drupal theme ever and is completely free. The theme balances speed and search engine optimisation with a full feature set. The theme is based>Features and Screenshots
* Speed Optimisation
* SEF Optimised Layout
* Advanced Colour Selection
* Suckerfish Dropdown Menu
* 8 Preset Styles - Light / Dark Variations
* 18 Block Regions
* W3C XHTML 1.0 Transitional. W3C CSS 3 Valid
Search Engine Optimised Layout
The structure places the main content before the side columns in the code hierarchy which is beneficial for SEO purposes as your primary content is crawled first by the search engines such as Google.