I casually use my rapidshare premium account for downloading and it was pretty annoying to not have any automated mass link downloading for Ubuntu as it was Flashget+Flashgot combo under Windows. After testing alot download managers and scripts, here I have my working way:

Fİrst you need to download Aria:

sudo apt-get install aria

After that, install the Flashgot Firefox extension from here. Enable it and under options select Aria as the default download manager of Flashgot.

Lastly, run Aria, under options menu select authentication tab and save your rapidshare login info. There you go