Snopes.com But There's really no way they could know something that hasn't happened yet.
Thanks for the reminder.
Snopes is partisan Left. And they admit that they influence whether a "rumor" is true or false by their synopsis/claim framing statement.
Additionally, they are willing to make excuses and allowances. For example, they are still unwilling to call Hillary a liar in saying that she was named after Sir Edmund Hillary. Without any evidence to the contrary (proof that young Hillary WAS told this deliberate lie by her mother) they claim that it is possible that her mom originated the lie. So much points the other way on this one.
Also things like the Target Vietnam Memorial and other protest letters did have origins in fact and weaselly apologies even though Snopes tries to label the whole thing a misunderstanding and unfair slam on Target.
So many examples. It isn't a very good site. Much of the apolitical urban legend research appears to be cribbed from Jan Brunvand's excellent books on urban rumors.