Lynn Viehl talks about the difficulty of coming up with titles that haven't been used: Title Recall .
When I was in college two books with the same title made the best-seller list just years apart: The Devil's Advocate, one by Morris L. West, the other by Taylor Caldwell.
Of course, some titles are sacrosanct. No point in calling your new novel Moby-Dick. Also, some authors are very good at choosing titles, others not so good. I've always thought Henry Miller was good at it, but not D.H. Lawrence.