Video Snooper is a free (Windows only) app that allows you to download video clips from an estimated 90% of all websites that have video. Why stop at just Youtube? Automatically locates video URLs and enables you to preview video prior to downloading. This is one application that downloads, mp4, flv, mpg, mpg2, and mov. It is not a browser plug in, so it works independent of your browser.
What's new in this version:
Version 188.8.131.52 fixes a problem with detecting and downloading Youtube videos caused by changes on Youtube.