What I do (and I've avoided duplicates this way) is search for bits of body text on Google News. You'll find duplicates, even if the two titles are totally different verbally.
For example, looking with the phrase "Swiftboat Vets," I found a story entitled
"Swiftboat vets, Kerry supporters speak in Greenville"
After searching for the body phrase "Two men who served with John Kerry," I then found another story, entitled
"Vietnam vets back Kerry's bid"
Only one word is common to both titles (FR's search function treats "Kerry" and "Kerry's" as different), but the text that I skimmed was identical or nearly so.
This method, while not foolproof, is a start. And while there are valid reasons for changing titles, I don't care much for changing them around just for variation or whatever. :p
Oh, and thanks, moderators!
That works (and I do it often, google news is pretty good, I personally like it better than yahoo news...plus they don't have the (search-web) thing that is really annoying), only if you don't mind not being the first in breaking news. In my normal life, I post threads, and faithfully search, I've only had a couple dupes, and yes, they were pulled as duplicates. I can't have the wraith of the mods on me, so maybe I'm overly cautious... I figure, it's posted, why bother again. But, then, I'm looking at it from a mod's point of view.