aheadWorks -
Layered Navigation
Optimizes the navigation and lets visitors search by categories, price ranges, color, and other product attributes.
Quick AJAX filtering
AJAX toolbar
HTML5-based URL change
Filter options
Layered navigation design
SEO parameters for filters
Price sliders and numeric filters
Multistore support

The module can be integrated with the following Magento extensions by aheadWorks: AJAX Cart Pro, Call for Price, Catalog Permissions