http://yagoohoogle.com/ I think it's really cool, espeically for the fact when you search for anything it gives you the Google results on the left hand side of the screen and the Yahoo results on the right!! Split-screen - genius
Yahoo has actually implemented google's results into their own search. Google uses what is known as spiders, which are virtual robots that visit massive amounts of sites and then index them. You will also get results from the yahoo directory which is made up of sites that have been gathered by actual people. Now they have merged the two together so when you get your results in yahoo it is actually a combination of the results from google and the results from the directory.