Open Source Cinema lets you create your own videos online, remix media that you have on your computer, as well as remix other people’s media from places like YouTube and Flickr.
Very nice Open Source video editor: http://fixounet.free.fr/avidemux/
Avidemux is a free open-source program designed for multi-purpose video editing and processing, which can be used on almost all known operating systems and computer platforms. Avidemux is my personal favorite because of its simplicity yet wide range of tools. Avidemux lets you do just about everything under the sun. It supports many file types, including AVI, DVD compatible MPEG files, MP4 and ASF, using a variety of codecs. Avidemux is available for Linux, BSD, Mac OS X and Microsoft Windows under the GNU GPL license.