Tag Galaxy is a visually cool site that allows you to explore relationships between words. Type in a word and the screen becomes a floating model of a galaxy with the original word at the center and words that are similar or associated with it orbiting around it.
If you click on the word in the center, a globe populates with pictures from Flickr that are tagged with that word. If you click on one of the other words that are orbiting around the original search word, you will get a combination of the terms and pictures related to both, as well as a new galaxy model with further choices of related terms. The more orbiting words you choose, the more specific your pictures will be.
Tag Galaxy is great way to visualize word and idea relationships.