The Trinity is a foundational Christian doctrine, much neglected and mostly misunderstood. In this post I will direct you to a debate (two videos) between a Trinitarian (James White) and a oneness Pentecostal (Robert Sabin). I watched the first and have yet to see the second. There is a third that is not available but can be found at Alpha and Omega’s website as an MP3.
I also highly recommend a book entitled Experiencing the Trinity by Darrel Johnson. A nice job of making the doctrine accessible without compromising the weight in his expression of God as one being in three persons.
I have also always been impressed with John Calvin’s treatment of the Trinity in the Institutes. You can find the Institutes and many other Christian Classics online and free at Christian Classics Ethereal Library – I highly recommend that you spend some time there.
There you have it.