I discovered Fluidr a few weeks back and have grown to love it. Basically, it's a simplified Flickr viewer that presents interesting photos for you to explore on a daily basis. Sure, you could find interesting photos on Flickr itself, but this is presented as a never ending stream that you can scroll through forever. And it integrates with your Flickr account so you can comment directly from Fluidr rather than having to go to the Flickr page for an image. Check it out at Fluidr.