I show videos from Discovery Education for science, math and social studies. There are many great videos that help the students understand the concepts being taught in these subjects. It is easy to search and narrow the search by grade level and media type. The most helpful thing on Discovery Education is that the videos have teacher guides and black line maters.
Copyright is ownership of material and work. Copyright only lasts for a certain amount of time, so older material may not be covered by the copyright law and may be part of public domain. Material that is in the public domain can be used by anyone. However, fair use says that material can be used if only a small amount is used and it is used in a criticism or parody. Work can also be used if it is transformed, re-purposed, or something is added. Copyright is difficult for students to understand. I don't fully understand copyright laws, so I can't really effectively teach copyright to my students. Students often don't understand why they can't just Google something and use whatever they find. It is important to teach them to use Flickr or Picasa instead of Google.
Dropbox would be useful to give students one place to get files, media, or pictures for projects. These files could be shared among classmates and accessed from anywhere.