1. SweetSearch is a search engine that returns only results that have been reviewed by a panel of educators, librarians and research experts and deemed appropriate for students. Recently SweetSearch incorporated several more specific search engines in the area of social studies, biographies, elementary searches and more. When I searched on SweetSearch I liked the fact that like Google, clicking on a search result gave me a preview of the webpage before I went to it.
2. Search Cube is a site I recently found and I really think this is a great way for students to start a research project. On this site, which is also powered by Google's search engine, you type in a search term and the results are brought back to you in the form of a cube of images. Mousing over these images on Search Cube you will get a preview in the sidebar of that site, video, or image. You can then choose that link or continue to scroll around the cube. Search Cube is what I envision searches to look like in the near future as websites, journals, images, video, etc. are all lumped together in one search engine.
3. Twurdy is a search engine that is powered by Google and uses a complex algorithm to to determine a page's readability level based on several factors including how many syllables each word has on average or the number of words per sentence. Twurdy is an excellent resource for all of the varying levels of readers you have in you class.
Besides search engines there are other ways to learn more about the topics you are researching. For example Explania is a great site with animated explanations, Qwiki is another site that uses video to review your search term and yet another is one of my favorites called Common Craft which uses stop motion animation to explain difficult concepts in an easy to understand format.
Help your students become more efficient searchers by posting links to these search engines on your website. You can also model their use in class and discuss with them why these search engines are a good place to start. Remember that it is always important to fact check and use more than one source when learning about something new.