As told by Saji89, FlareGet would be an ideal choice for you as
FlareGet is a full featured, multi-threaded and multi-segment download
manager and accelerator
But the free version in Ubuntu software center does not support "Browser integration", you need to pay $10 to get browser integration plugin. I guess without browser integration, download manager won't make sense.
So here is the workaround. I have tested it on Firefox 18 and it works like a charm.
- Just go to Firefox > Tools > Add ons > Extensions.
- Search for addon "FlashGot", install it and Restart the Firefox.
- Go to Tools > Add ons > Extension > Preferences for FlashGot.
- On General tab, choose FlareGet as download manager and check the check-box against "Show in Context Menu"
- On FlashGot tab, choose FlareGet as download manager and check the check-box against "Show Toolbar button".
- Now restart the Firefox. FlashGot will act as Firefox integration plugin for FlareGet.
Just right click any downloadable link and choose FlareGet. If you want you download video from YouTube just play the video, an icon will appear on right most side of the tile bar. Just click on that icon and FlareGet will capture and download the video.
I love Firefox so this is enough for me. Something similar can be worked out for Chrome.
FlareGet + FlashGot on Ubuntu == Internet Download Manager/Orbit downloader on Windows