I was just re-reading my post about the demise of Grokker. I failed to mention that there is another search engine that clusters its results. It is called Clusty.com. It doesn't have the visual maps that Grokker had, but it still can be helpful to have the search results grouped together.
Also, as an update, I think I have at least 2 students signed up to take my research strategies class at Rivendell College Spring semester. I'm so glad there will be at least 2 students who will learn to evaluate sources, develop good research topics/questions and how to find sources in many different formats. I'm looking forward to teaching and I hope my students learn some lifetime skills.