I really like the apps that package up a popular tool to allow a user more flexibility. MiniTube, licensed under the GNU Public License, allows for you (on Mac and Linux–Windows is coming) to bypass the browser and type searches directly into a desktop app. Then it delivers and plays YouTube videos directly on the desktop. It also lets you download them easily, for portable players or later use.
The great thing is they release source code, allowing individuals to take what was created and make it even better. In the comments section folks asked for playlists and a variety of other things. These thing could be done on closed source apps, but often they would take awhile or may not even get completed. With an OSS app, you can do the additions yourself, or many others can. Just the beauty of OSS.
Find MiniTube here: