UGet, is one of the best download managers available for Ubuntu with almost all features you would want from a download manager - pause/resume functionality, multi-threaded downloads, clipboard monitoring and scheduling etc.
Now UGet 1.7.3 has added app-indicator support so that now you can use it with Ubuntu 11.04 too. Also it now uses Aria2c as back-end for faster multi-threaded downloads.
This is a development version, you can download stable version from software center.
Add the PPA and install UGet 1.7.3 by running following commands (for Lucid, Maverick and Natty):
sudo add-apt-repository ppa:plushuang-tw/uget-devel
sudo apt-get update
sudo apt-get install uget
Also read How to Integrate UGet with Chrome/Chromium