Grokker - A Graphical Search Engine
Rather than the usual textual listing, search results are displayed in a map containing nested circles and squares. Circles represent categories into which results are grouped. Categories may contain many levels of subcategories. Larger circles contain more subcategories and links than smaller ones. Click on a circle to zoom in on a subcategory.
Squares are web links that result from your query. For a summary of the contents of a link, hover over that square. The link itself appears on the right, along with a thumbnail image of the page.
Very neat, especially for visual learners. But I wish that they'd lighten up the page a little. The black background makes it hard to see.
Thanks to my UW-Madison Libraries colleague, John Wanserski, for the tip.