Google Images has a nice little feature with that you can search images showing face. To use google images face search you need to enter &imgtype=face to the end of the search string. Ex: Normal search http://images.google.com/images?hl=en&q=britney, for face search, http://images.google.com/images?hl=en&q=britney&imgtype=face
I stumbled over Facesaerch.com which allows you to browse these images in a coverflow interface. Enter any search string in search box and it will retrieve images from Google Images and shows in a coverflow interface. You can set options to like safe search and others using options. The interface looks cool, but there is one limitation, it won’t show thousands of images available via Google images, it will show only few images retrieved via Google API.
Another cool feature of facesaerch is it supports viewing pictures in RSS feeds as coverflow. You can try this Flickr RSS to see how it works.