Minitube is an application for watching YouTube without Flash.
Minitube 1.2 beta was just released, bringing a much requested feature: Gnome multimedia keys support as well as YouTube video downloads.
(Downloading a video - Minitube 1.2 beta)
The videos are downloaded into your ~/Videos folder, but you can change the location once you start downloading your first video (see the above screenshot).
Minitube 1.2 is almost ready and you can help by translating it into your languange. Details @ Flavio's blog.
Install Minitube 1.2 beta in Ubuntu
Minitube 1.2 beta is available in the WebUpd8 PPA so Ubuntu (Karmic, Lucid and Maverick) users can easily install it using the following commands:
sudo add-apt-repository ppa:nilarimogard/webupd8
sudo apt-get update sudo apt-get install minitube
Once installed, you can find Minitube under Applications > Sound & Video.
If you're not using Ubuntu, you can download Linux 32bit binaries @ Minitube website along with Mac OSX files.