While there is no way to know to be completely sure if someone you are dating or interested in may have a history as an abuser, there is a website which is compiling a list of known offenders. This list is of individuals who have had a legal restraining order or protective order served against them.
This is not completely fool proof, of course, but it is certainly a lot better than no information at all. I would also encourage anyone who reads this and knows of offenders who should be added to the list to add them! Remember, however, this list is for legally documented offenders only. I know many abusers never are legally found guilty, but without legal documentation, adding someone to such a list becomes legally libelous.