Good open source Video Editors?
VLMC is a non-linear multitrack editor. It's based on VLC and inherits a pretty vast format compatibility from that. The UI is a little rough, but it gets the job done.

Lightworks is a more recent project and seems polished. It's rooted in broadcast editing, so a large number of familiar codecs are unsupported. It supports Matrox codecs, which you have to install separately, so you'll have to convert your video to Matrox AVIs first.

Avidemux is a simple editor, good for trimming and small tasks. In my experience, not very stable on Windows, OK on Linux.