One plugin is probably as good as another, but I am currently using the Flash Video Downloader plugin for Chrome. When you add it to Chrome, it installs a little downward pointing arrow which turns blue when it detects media to download. If you click it, it then shows you all the media that it has discovered on the page, so make sure you choose the highest quality when downloading. One thing I like is that it offers you to save to a location, and captures the name from the page title.
Definitely worth installing if you like downloading from Porn Sites.
