Sorting post by a star rating

Hi guys, I’m experimenting with using word press as a kind of directory. Im using a woo themes theme called city guide as it has 90% of what im looking for build in.

Here is the website in question that im working on http://www.digitalblusky.co.uk/vwl/arts-culture/

I need to be able to allow the user to re-order the posts based on a star rating preferably being able to select between the star rating and alphabetic order using a drop down menu. Can anyone suggest the best way to go about this? Are there any plug-in that might help?

I would really appreciate any help.

Thanks