I say the "generic" -- Memory eternal! May God rest his/her soul in peace! Of course, if you really want to bring the hope of salvation to people, you need to talk with them a bit more and this requires a bit of skill and knowing when to speak about these things and when to keep quiet (if people don't really want your hope). Personally, I prefer befriending them a little so that I can get access to their souls and actually be welcome.
Also, it is a delicate issue and you don't want to say something like "they are in heaven now" because it's superficial and can't really cover the magnitude of the mourning. There is no real formula for dealing with this, or else people would apply it all the time. Being there for someone and telling them that, or just being silent, would probably accomplish more than the words.