Compfight: Web 2.0 power search for Flickr
Compfight fits all the most important Flickr search options into its minimal design. You can switch between tags and all text, turn Creative Commons on or off, and decide whether clicking thumbnails will take you to the default photo page or show the original size. It takes some fiddling to do all of this at Flickr.com, but Compfight uses the Flickr API and makes everything easy.
Oh, and about those thumbnails: a blue line at the bottom lets you know that Flickr has an original photo, and you can mouse over it to see the photo's dimensions. It looks so good that you might be tempted to completely give up going to Flickr.com for your searches.