My new friend Harold Jarche told me about this on the conference I was recently at. The Creative Common Search allows you to search for content licensed under the Creative Commons license. The search site also contains a good overview on what the license means.
Some additional commentary: So what does this mean to you? Well, if you’re conscious about where you material comes from (i.e. whether or not it’s legal to use, modify, etc.), you’ll know that it’s often difficult to either get permission or know whether you need it in the first place. This search narrows the content to only that which explicitly states what you can and cannot do.
If you’re a student looking for things to reference for an assignment, project or essay. You can now find material that you’re teacher will not hassle you about copyright issues. 
If you’re a teacher, you can now find images, videos and other materials for your class activities, lectures, assignments, etc. without worrying about whether or not you have the in-class rights.
If you’re a web developer, you can find content to use for your web projects that you don’t have to pay for and are not going to get sued for.
etc., etc…
Copyright issues come up all the time at my school (and every other school I’m sure). This is going to help. Thanks, Harold!
I think that every student should know about this tool, as it makes class projects much easier.