The Mega Man fan in me says one of the Hunter Commanders, like Sigma or Signas, although, to be honest, Sigma ends up somewhere over seven feet, last I remember.
Past that, I would say that it really depends on the genre that you're going for: if you want it to be someone from a cartoon, a movie, a comic series, etc., although the sheer number of posts prior to mine bring up several good suggestions.
Honestly, I'll admit that people that are over 6' usually bring to mind either the muscle-bound fighters from some of the classic side-scrolling fighter games or someone dressed up in a mech suit. That, of course, can vary from Transformers and Voltron (I saw someone post that) to the various mech suits that exist, such as those from Gundam or Evangelion.

or one of the Amalgams from Blassreiter, if you're familiar with that anime.
Just a couple of suggestions.
Midnyght Saber