filter posts on frontend by meta data (customs fields)

Hi,

I am building a review site for fringe plays. I have set up a review (post) input form using advanced custom fields and now need to be able to sort the posts by those fields. ideally i’d like two drop down menus, the first to select what to sort by (genre,author,venue, etc) and the second with a list of that custom field’s options.

I cannot find a plug in anywhere that does this… please help!