"The National Biological Information Infrastructure (NBII) has updated its search engine to search multiple databases at the same time, and now also returns clustered results. You can try it at NBII.gov. "

Source: ResearchBuzz, 9/3/09

From "About" NBII :

The NBII Program is managed by the U.S. Geological Survey’s Biological Informatics Office, and "is a broad, collaborative program to provide increased access to data and information on the nation’s biological resources. The NBII links diverse, high-quality biological databases, information products, and analytical tools maintained by NBII partners and other contributors in government agencies, academic institutions, non-government organizations, and private industry. NBII partners and collaborators also work on new standards, tools, and technologies that make it easier to find, integrate, and apply biological resources information. Resource managers, scientists, educators, and the general public use the NBII to answer a wide range of questions related to the management, use, or conservation of this nation’s biological resources."