With the launch of Microsoft's new Bing search engine, a Microsoft employee must have been wondering the same thing - so he created a neat Blind Search tool (and states this is not a Microsoft project).
Type in a search term, and Blind Search shows you the results from Google, Yahoo and Bing - but without telling you which engine produced each list. So without brand bias, you decide which results list includes the most relevant websites.
And the best part is the reveal, when you "vote" and see which search engine the results came from.
I played a bit, and surprisingly, Google didn't always provide the most relevant results. As the creator states, this seems most useful as an observational curiosity, but it certainly is fun and interesting (or, it gives people a way to find pron three times faster).