In one of our previous Ask TUAW columns we addressed a question about downloading Flash videos from sites like YouTube and Google Video. We mentioned several shareware programs to do this including TubeSock and yFlicks, however recently a free solution has come to my attention called simply the Flash Video Downloader from Tesseract Software. The interface is very simple: you just copy and paste the URL from your browser for the page that the video appears on (i.e. you don't have to know the exact location of the video file, just the main page URL). The Flash Video Downloader apparently consults videodownloader.net for the actual file location and then sucks it down to your computer. Of course once it's downloaded you'll need VLC or something similar to play it. You can also set up a series of pages as a batch job and the Downloader will do its thing in the background downloading each video, then send up a Growl notification when it's done.
The Flash Video Downloader is not as slick as some of the commercial solutions out there, but it's a free download, and does get the job done.