The Zappos' search engine provides a nice results filtering interfaces that presents the user with facets for refining their search. The user can click on the terms at the top of the search results page to narrow the set, and a breadcrumb trail shows the selections they've made. Each term in the breadcrumb provides a checkbox to remove any one of those selections and broaden their search.

1. Users run a search using the site's global search box. In this scenario, I used the term "Running" and we're viewing the search results page that provides facets for narrowing your search. Options for sorting are displayed above the results.
2. I've clicked a few terms in the following facets: Product Type - Shoes, Gender - Men's, Size - 8.5. A breadcrumb list is shown above showing the refinements I've made to my search and the results have been updated.
3. I've added a few more refinements, and the result set has been reduced from 908 to 19.
4. The breadcrumb trail showing what I've searched for provides checkboxes to remove terms from my search, and this screen shows that I've removed the color Black from my search.