"Popcorn Maker makes it easy to enhance, remix and share web video. Use your web browser to combine video and audio with content from the rest of the web — from text, links and maps to pictures and live feeds. "
Well it's free for one and looks quite advanced for a free app.
I've use iMovie which is fairly good, then I'm using Final Cut Pro which is like the mother of video editing and incredibly awesome. I'm still learning it and it's very addictive.