The Dropdown attributes module for Ubercart allows attributes to be conditionally displayed depending on the options chosen for other attributes. This avoids presenting attributes to a customer which do not apply to them. The current release for Drupal 7 utilizes Drupal's AJAX form handling for both the administrative and user interfaces. There is complete support for select boxes, radios and checkboxes and for text fields as dependent attributes.
Personnel for Gaia Environmental Sciences developed this module in 2010 and have been maintaining it and ported it to Drupal 7.
Check out the demo.