I've defended the Trinity until I was blue in the face. But I think the most sense came from an email that was sent to me by Ray Franz. He said that while he has never come across historical evidence that the 1st century Christians ever believed in the Trinity, he also recognizes that the Bible seems to teach things that could support the idea. However, he said that he prefers to remain silent where the scriptures are silent.
I agree with Undisfellowshiped that there are MANY MANY scriptures that seem to prove the Trinity. There are scriptures that call the Holy Spirit God, Jesus God, and the Father God. However, the EXPLICIT doctrine is not given. Why is this? I think that maybe it's not really important to know the very nature of God.
Do I understand eternity? No. How could I? It's beyond my frame of reference. Do I deny that God is eternal? Never. Do I understand the Trinity? Not completely. But if God wanted to exist in the form of a Trinity, could He? Yes he could.
I think the tendency to be dogmatic on both sides is very prevelent. I have been on both sides of the issue. Right now what seems to make the most sense to me is that I love Jesus. I love the Father. And I love the Holy Spirit. Do I understand their nature? No. But I love them and their roles all the same. Will God judge me for not understanding his nature (which is beyond our understanding?) I really hope not. I just want to follow the Christian life and love God for who He is. Beyond that, I pray that He will bring me into a greater knowledge of Him one day.