Wiki Lyrics is a complete Amarok script which allows fetching of song lyrics from various websites, like AZ Lyrics, Leos Lyrics, Lyrc, Jamendo and several more.
First you will need to install the dependencies, so issue one of the following commands:
apt-get install ruby1.8 libqt0-ruby1.8
apt-get install ruby1.8 libgtk2-ruby1.8
apt-get install ruby1.8 libtcltk-ruby1.8
Only one of those is needed. Next, open Amarok and go to Tools -> Script Manager, press Get More Scripts, select Wiki-Lyrics from the list that appears and click Install.
After the script is installed, select it in the Script Manager and click on Run.
Wiki-Lyrics should be installed now.