Myself, I think my favorite "minor" NPC is good old Brother Sarno, the greeter at the Cathedral of Light. This is a guy who, day in and day out, stands at the entrance of the cathedral sanctuary in Stormwind with a smile on his face and joy in his heart, greeting people as they come in the door. It doesn't matter if you're a Paladin or a Warlock. It doesn't matter if you're a level 5 exploring Stormwind for the first time or a level 70 coming to receive a blessing from Archbishop Benedictus before heading out on your latest crusade. No matter who you are, if you come to the cathedral, he will give you a smile and often a greeting. I've even seen him greet stealthed Horde Rogues.
That is Brother Sarno. He never tires, he never complains, and he will treat all people with dignity and respect regardless of race, class, level, or political affiliation. He sees all, no-one can hide from his gaze. This man is the purest and most faithful representation of the Light that I have yet to meet in all of Azeroth. I sometimes wonder if he's actually a Naaru in disguise, or at least the true archbishop and head of the church, disguised so as to throw off assassins. I think the world would be a better place if everyone tried to be just a little bit more like Brother Sarno.
Well, enough of me gushing about Brother Sarno. Who are your unsung Heroes? What NPCs keeping rocking their jobs day in and day out and deserve a little bit more praise for it?