I actually liked Bing's image search and have been using it lately, but then Google says "Bam! Back at you MS!" This is a pretty cool twist on image search. More from Google's Official blog:
"Back in 2001, to give people a new, quicker way to find images, we launched Image Search. When you do a search for [eiffel tower] you'll find an array of images of the tower in the daytime, in black and white, at sunset and more. With Similar Images, which recently graduated from Google Labs, you can click "Find similar images" to narrow your search to, say, pictures of the Eiffel Tower lit up at night. Today, we've launched an experimental feature in Labs called Google Image Swirl, which builds on new computer vision research to cluster similar images into representative groups in a fun, exploratory interface..."
Here are my results from "Iguacu Falls":