While it's not a free program, Corel's Video Studio is what I use. One, you get multiple tracks of audio and video, and can even have video inserts and bluescreens with it. And most importantly for when you work with HD sources, all the transcoding makes use of your computers graphic card to do the incredible amount of compressing/decompressing. So the computer doesn't have to spend an hour generating hugenormous uncompressed video files on your hard drive for you to be able to edit them anymore -- it uses the GPU and you work with the files in their native format as if they were cached uncompressed stuff. I went from a core2duo rendering 1 hour of HD video in 10 hours of uninterrupted time (I just went to bed), to rendering an hour of HD video in 12 minutes.
Not bad at all for 50$.