Direct link: http://extensions.activo.com/seo-friendly-categories-for-magento.html
Do you have a big store with a lot of product subcategories? By default Magento generates a really long URLs for these subcategories. This can really kill your SEO because it gets translated to how ‘deep" your pages are. Search engines lose interest after a certain level therefore, flat categories will allow you to gain this control once again and be able to optimize better for SEO.
This simple FREE extension can flatten your store URL structure and drastically improve your SEO in just few simple clicks.