I'm still working on my monument list.
My own rules take out one of the easiest choices as a great leader IMO - Gandhi. Doubt that MLK would've made top 4 for me, but he would have garnered consideration had the criteria not eliminated him as well. Mandela would have been an easy one for me 20 years ago; now I'm not so sure.
On my short list at this point would be Cyrus, Genghis Khan, Alexander, Augustus, Churchill, Napoleon, FDR, Washington, Lincoln, - can't help but feel that list shows I'm a little too deep in recent (primarily North American) history and shallow everywhere else. Need to learn more about Che Guevara, Salahuddin, Mao Zedong. And I'm sure there are lots more I'm missing - looking forward to learning from all of you.