Blow Up uses the public Flickr API tp create a slide show presentation that allows your images to be seen in fullscreen mode while still showing thumbnails of the other images in the slideshow and navigation to your sets, while maintaining your image quality (or, in my case, showing me that, when blown up, a lot of my pictures are not quite focussed). It's a very clean UI.
The service is free and doesn't require anything other than your Flickr username to get started (I do wonder if they're storing those). because you are not logging in, Blow Up only shows images that you have set to public viewing. Other functionality include being able to download the Blow Up app to display your Flickr images on your other websites.