Peter Kreeft, professor of philosophy at Boston College, includes on his website a great essay called Evidence for the Resurrection of Christ. It's somewhat inappropriately named, however, since most of the essay (it's actually a chapter from one of his books) actually focuses on refuting alternate theories about what happened at/after Jesus' crucifixion. Here's an excerpt from his introduction:

The question is this: Which theory about what really happened in Jerusalem on that first Easter Sunday can account for the data? There are five possible theories: Christianity, hallucination, myth, conspiracy and swoon.

Thus either (1) the resurrection really happened, (2) the apostles were deceived by a hallucination, (3) the apostles created a myth, not meaning it literally, (4) the apostles were deceivers who conspired to foist on the world the most famous and successful lie in history, or (5) Jesus only swooned and was resuscitated, not resurrected. All five theories are logically possible, and therefore must be fairly investigated—even (1) ! They are also the only possibilities, unless we include really far-out ideas that responsible historians have never taken seriously, such as that Jesus was really a Martian who came in a flying saucer. Or that he never even existed; that the whole story was the world's greatest fantasy novel, written by some simple fisherman; that he was a literary character whom everyone in history mistook for a real person, including all Christians and their enemies, until some scholar many centuries later got the real scoop from sources unnamed.

Read on for more. Highly recommended.

Further reading:

• Facts Concerning the Resurrection – Resurrection expert Gary Habermas examines the facts that historians (including skeptics) agree upon and what we can conclude from them.