Murfroofer: I note that Jay aka EET is the only one who has answered your question so I want to put my 2 cents worth in, because, since the verse he quoted is the only place that seems to answer your question, it is incomplete and leaves you up in the air as to whether or not he changed his name.
My answer would be "None" because that accurately answers the question. There are no books, chapters or verses that tell us that Paul changed his name from Saul. And then I would have quoted Acts 13:9 as Jay did as the only place where the name change is even recorded.
ACts 13:9 says "But Saul, who was also known as Paul....." (NASB) contains an informative statement, probably better served if it had been put in parenthesis. Apparently it didn't bother Paul because from that point on in Scripture he is always referred to as Paul and he began most of his letters identifying himself as Paul, and he signed them all as Paul.
Jay and I agree.....only I think he did not go far enough in his answer.