Mix videos, GIFs & sounds!Weavly enables you to create video mashups and remixes with material you find on YouTube, SoundCloud and Loopcam. It's free to use and according to the Weavly blog, "you don't have to worry about uploads, downloads or copyright issues".
Browse samples on the site or create your own. "Weavlies" are public and viewable by anyone with the URL. You can upload your own original dialog or music tracks using SoundCloud and combine it with found video on Youtube or your own uploaded clips.