YouChoob is a tiny portable application that makes it quick and easy to download a local copy of your favourite YouTube video.
Just paste the video URL into the program, click Download, and after asking you where to save the video, YouChoob will immediately start downloading the file. It automatically chooses the highest possible resolution, which is handy, and a small preview window shows an early frame, useful as reassurance that you're downloading the right clip.
And if you're looking to grab a whole bunch of videos then there's even easier route in YouChoob's batch download feature. When you find a video you like, simply paste its URL to the clipboard. YouChoob will automatically detect this, add the URL to the list, and begin downloading the file.