Google's a really big sandbox to be digging through if you're looking for only the most legitimate material for a research paper. SweetSearch ranks up primary sources and credible sites, like universities and public repositories, for students looking to narrow their search.
SweetSearch came about as the byproduct of making findingDulcinea, an aggregator that terms itself the "Librarian of the Internet". It's a database of about 35,000 websites vetted by researchers, librarians and teachers, with priority given to spots like the Library of Congress, Smithsonian and other public and academic sources. It sweeps away the pseudo-science, forums and sites that read like paraphrased summaries.
SweetSearch offers their best pitch in a blog post for how their engine beats Google for scholarly stuff.
Aside from Google Scholar, where else should students look when they're looking to do some deep digging on the web?