I think Michael Dorn voiced a non-hostile supermutant in FO2. Given how long those guys can live he's probably reprising that role for FONV. He's actually done quite a bit of voice work as I recall; animated shows and video games. As it happens I was just playing Saints Row 2 and he had a rather significant role there too.
Matthew Perry is a bit of a surprise, I don't think I've spotted him in anything since...I suppose it must have been a guest shot on Scrubs about 4 years back!