Google Image Swirl is another service from the Google Labs that organizes image search results based on their visual and semantic similarities and then clusters them into related "swirls." It uses metadata and is similar to Bing's VisualSearch.
Students can use the Wonder Wheel feature for some brainstorming on a topic. There's also a Timeline feature that allows you to scan historical references to a topic and then focus on a specific date(s).
Like other services in the Labs, this one could disappear at any time - but there always seems to be something new.