Is there a complete list of early Christian texts including those that are not in the New Testament?
No. Various followers of Jesus were reading many different texts in the first few centuries. (The phrase “followers of Jesus” is used on this website instead of “Christian,” a term that appears only three times in the New Testament.) The list of the books used for the New Testament developed only gradually over a period of centuries. Texts continue to be discovered. There are, however, several collections you can consult. See the Resources page.
Here is a rough organizational chart of the best known early Christian texts, illustrating the relationship of canonical and extracanonical texts: