[@Eklispe] Very good question! I added a Weakness section to Luke's profile, but removed it due to uncertainty... I think the things I originally added were: silver (within the bloodstream), fire, and wolfsbane. Silver being the most potent, of course. Wolfsbane would be used in a torturous like fashion, making Lycans completely uncomfortable. Probably one of the most painful things to experience is being in contact with the stuff. Fire I would think would be more psychological if anything, but I would also imagine that fire is more dangerous to a Lycan compared to a human. 

Of course, just some random stuff that I just thought of. :P Not my choice to make. No idea what Vampires would/should be weak too though.