It seems that as of late the Enemy Territory's masterlist is down. As a workaround edit the hosts file and add a new masterlist provided by etmaster.net.
In FreeBSD and Linux distributions, run the following command:
# echo "18.104.22.168 etmaster.idsoftware.com" >> /etc/hosts
Fire up ET as a new list of servers will be available.
Major thanks Paul at the Splash Damage forums for providing a solution ;)