We recently released our new Category and Search pages with AJAX filtering. The design team gave us wireframes for how they wanted it to look and I discussed implementation strategies with the Technology Director.

What we ended up doing was creating AJAX filters that use Magento's built in Faceted Search functionality. So each "dropdown" filter is a filterable attribute in Magento with a custom built presentation model. I created a new AJAX controller that handles the callback. The controller's response is a JSON message that contains the new HTML to be displayed: one for the filters and one for the page content.

I used jQuery to create the flyout animation and to handle the AJAX requests.