Taylor Marshall of Canterbury Tales has an interesting post up about the "direction of causation", as it were, between Christianity and Neoplatonism. On any reading of the Church Fathers it is a relatively easy matter to point to various elements of their metaphysics and theology--especially terminological elements, but also some substantial ones--and draw parallels to similar elements in Neoplatonism. Taylor points out that Plotinus, who is often cited as the "founder" of Neoplatonism, was taught his Plato by the Christian Ammonius.
Although it is an interesting point, I think it's worth pointing out that Platonism, as such, was unavoidable in antiquity, especially in the Eastern Mediterranean, and talk of direction of influence will always be hopelessly underdetermined by the data. It is possible to find possible Platonic elements even in the writing of St. Paul, if one uses one's imagination, and of course, it is not only possible, but indeed quite likely, that a man who was educated in that area at the time that St. Paul was getting his education would be learning from men who had read some Plato, so....
The temptation by some Christians to dismiss the influence of Platonism is strange to me. I once knew a man, a very old-fashioned Catholic, who would condemn any view held by Protestants. I asked him, "What about the Trinity? Protestants believe in the Trinity, should we reject that view, too?" I was basically kidding, but the guy was thoroughly stumped. That's what happens when you wed yourself to a particular ideological view of history. The same man was not in the least bit disturbed by St. Thomas Aquinas's frequent allusions to "The Philosopher" (i.e., Aristotle). "That's different", he would say. "Aquinas was merely using Aristotle." The idea being, I guess, that there are certain kinds of cases where the idea isn't merely being "used".
To me, it doesn't matter where the idea came from, just so long as it's true (or, indeed, useful). Some of Plato's ideas were manifestly true, even from a Christian perspective (for example, the idea that the Good transcends being, or the idea that morality is not a matter of mere subjective experience). It is a mistake to maintain that truth began with Christianity, or that Christianity could never learn from Platonists. To what extent and in what specific ways Christianity learned from Platonism will, necessarily, remain somewhat mysterious, but that it did cannot rationally be denied.