MediAvatar Free YouTube Video Download is a free video downloader that's a little different to most of the competition.
One major plus point is that it comes with a built-in browser. Which means you don't have to worry about whether it works with your browser of choice (hopefully without introducing annoying plug-ins or add-ons that will slow you down): just launch the program and it'll open at YouTube, ready to locate whatever videos you'd like to download.
Using the program is then very straightforward. Just browse YouTube as normal, entering search terms or visiting your favourite channels, and when you find something you need, click the Download button. Free YouTube Video Download will immediately fetch a permanent copy of the movie for you, which can then be viewed at any time with a speedy double-click (as long as you've an FLV-friendly video player, anyway).
It's easy to get carried away, of course, and before you know it you could have a download queue extending far into the distance. This doesn't have to consume all your bandwidth, though. MediAvatar Free YouTube Video Download can optionally impose both a maximum number of simultaneous downloads, and a maximum download speed, so if you tweak these settings carefully then you'll be able to download clips without this significantly affecting your browsing or other online activities.