Based on what your information needs are, NoodleTools provides a directory of search engines suggestions. An excellent place to help students interpret their information needs.
ThinkTank is an electronic performance support system to help students narrow down research topics and create keyworks and searches to move the research process forward.
A FANTASTIC resource for students (and teachers!), Wordnik allows you to search for a word and then shows its definition, example sentences/uses, etymology, pronunciation, tweets with the word, and photos from Flickr that are related... wonderful for all learning styles.