Avidemux is a simple video editor which is extensively used for video applications in Ubuntu. You can cut ,filter and encode your video task. It has support for AVI, DVD compatible MPEG files, MP4 and ASF as it has pretty much codecs bundled.
Cinepaint is a very useful and user friendly video editing application which supports 8 , 16 bit and 32 bit color channels. It is also used for retouching motion pictures frame by frame with features like wire background plates, rig removal, dirt removal, render repair and painting 3D model textures.
How can I ever miss this one? Well, Cinelerra is yet another free Ubuntu app which can do capturing, compositing, and editing of audio and video files with sample level accuracy.