4 Comparison Search Tools You May Not Know About … But Should by Matt McGee, Search Engine Land (Dec 29. 2009)
These comparison search tools show results from different search engines side-by-side - making it easy for you to see the differences.
+ Search3 - Google, Twitter, Bing - you can change the order and substitute eBay for one of the columns. Does the same for image search but the choices are Google, Bing, Yahoo and Flickr.
+ Googawwho? - - pick 2 out of 8 engines - but there are only four you'd want: Google, Bing, Yahoo, Ask.
+ Panabee - two side-by-side from Google, Bing, Twitter, Amazon, Wikipedia, and others - shows the actual search results page.
There's also a tool for comparing maps. MapsCompare - Maps Compare lets you compare the map search results of four sites on a single page: Google Maps, Yahoo Maps, Bing Maps, and Google Earth. This is much easier than setting up four windows.