How to filter the search/browse results by user selected subject

What I want to do is filter the results of the Item Search using a select input with a pre-populated list of Subjects (from a SimpleVocab). The Edit Page in the admin side does this, by displaying a select input populated with existing subjects. I want this so the user can choose to filter the public Item Search/Browse listing by subject. Has anyone tackled this before? I'd appreciate hearing how you accomplished this.

To summarize, I want the user to be able to filter the results by a menu where they can choose a subject from existing subjects to use as the filter.