Looking back when I first started investigating into Orthodoxy, I can't help but owe alot of debt to Fr. Hopko, who I listened to his podcast "Speaking the Truth In Love" religiously. He was/is so crystal clear about a lot of things and was so down to earth. I haven't listened to him in awhile, but I think I will go back and see what's new with him. Sure there are things he has said, theologically, which raises my eyebrows but on the whole I really can't thank him enough for how much he has helped me. Without him I am not sure if I would have ever become Orthodox. Almost everything he said just made me nod my head in agreement and that rarely happens much.
Fr. Stephen has a blog that I have gone back to over the years and was also instrumental in certain aspects. Fr. Andrew Damick had some great intro to Orthodoxy podcasts and also helped me understand how one comes to approach God and to understand him.
Some of the priests on this forum have been wonderful as well. Fr. Giryus, Fr. HLL, etc.
I admire His All Holiness and greatly respect him.
Outside of the Orthodox Church, NT Wright has played a role and I am shocked he isn't Orthodox yet. Never been a CS Lewis guy, I liked where he went with the Abolition of Man but I was not impressed with Mere Christianity.
I believe arguments matter and I just felt he didn't have strong ones.
Trying to think who else, would probably give the nod to Chesterton. I remember reading his book Orthodoxy and laughing all the time because he made perfect sense. Here and there I'll disagree, but Lewis tries way too hard to emulate him with his apologetics.
William Lane Craig was surprisingly important when I used to watch a bunch of atheist vs theist videos all the time before I even heard about Orthodoxy. In my eyes, at the time, he was an excellent debater and planted a seed that God really must exist. Then I read his website and was pretty impressed. I credit him with opening the door for me to finding the Orthodox faith.
Trying to think about any other Orthodoxy clergy. When I was at a Greek parish, His Grace Isaiah was magnanimous towards me and so was this assitant priest that was at the Cathedral. I have never seen that kind of meekness before in my life, I couldn't believe it existed.