There's a rather provocative article here about novel titles being "recycled" by authors. Mira editor Margaret Marbury is quoted in it as saying, "Most really good titles have been used before. It's very hard to find something completely original."
Title repeats do happen. After I published Heat of the Moment, I discovered that Olga Bicos also had a book with the same title. My editor shortening Dance Into the Fire to Into the Fire put me in a herd of other authors who have used the same title, including Don Pendleton, Che Ahn, Anne Stuart, Alexander Fullerton, Richard Laymon, Leslie Kelly, David Wiltse, and Jeffrey S. Savage.
I can't always avoid a repeat, but since the last two JH books I've been making a real effort to cook up titles that are unique to my work. Raiding old poetry for ideas, as I did for my titles If Angels Burn and Private Demon, seems to work best for me. When my publisher condensed my title Darkness Has No Need to Dark Need, I tried my method in reverse, did a search on the new title, and found a poem by Caroline Southey that suited the novel. Which I needed, because I could no longer use the fragment of Byron's poem with the original title as an intro verse.
I can't agree with the article because I don't think all the really good titles are gone. I think all the really easy ones are. If you want a title unique to your book, you simply have to work a little harder. I've recently begun searching The Library of Congress online catalog whenever I come up with a possible title. If I can't find it in LoC's 12 million title records, I figure I'm good to go.
How are you guys cooking up your titles and avoiding repeats these days?