Here are few Websites with a combined power of Google and Bing.
Bingle.nu provides the comparison of the two search engines(Google and Bing). So you can check Google and Bing search results at the same time.
This service is unique in terms that you can directly search for images in both search engines. And there is Twitter strip in between the two which is separating the two SERPs. You can search images in this website which provides search results of both the search engines simultaneously.
All the tools above display search results in vertical position, however, Bing-vs-Google has a option to display results in horizontal fashion which would be useful for large screen computers.
Compares both the search engines in different languages which makes it unique in itself.
Dogpile is the combination of Google, Bing, Yahoo and Ask.com. It shows the combined search of these search engines.