Without a doubt my favorite Firefox extension. Available in both Windows and Linux. The Video download helper. It lets you download videos from Youtube and dozens of other websites.
DownloadHelper is a tool for web content extraction. Its purpose is to capture video and image files from many sites.
Just surf the Web as you are used to, when DownloadHelper detects it can do something for you, the icon gets animated and a menu allows you to download files by simply clicking an item
For instance, if you go to a YouTube page, you’ll be able to download the video directly on your file system. It also works with MySpace, Google videos, DailyMotion, Porkolt, iFilm, DreamHost and others.
Go have a nosey, its a simple plug in for Firefox so a quick and easy setup.
A quick pokey paws shout out for this brilliant little application. Rummage through the Ubuntu repos and you will find Aria Download Manager. It does what it says on the tin, and a lot more.
I found it when looking for an app i could use to Que up a stack of downloads and then just download them one after the after. Aria does this well. waiting for one download to finish before automatically starting the next download in the Que. A huge convenience for me as i leave my PC downloading all the time. There is a bit more to Aria, it has a stacks of settings to make it behave how you want it to behave with downloads.
Its not very pretty, but hey you cant have everything. The interface is clean and simple (and easy to understand, a must for silly folk like me ^^ ).
It appears this isn’t being actively developed anymore though. The creator has moved onto making Aria2. So lets hope its as good as the first ^^
So, if your on Ubuntu or one of its derivatives, have a look in the repos.
There is a wiki page for it here : http://en.wikipedia.org/wiki/Aria2