A warm bath full of biological washing powder to break down the flesh and soft tissues, followed by a good long soak in Coca-cola to dissolve the bones. Job done, and you don't have to buy anything weird at the supermarket to give yourself away.
What? Oh.
I tend to leave the dead where they fall in games, as a warning to others of the fate that awaits them mere seconds into the future and give them a chance to get their affairs in order and/or make peace with their programmer. Even in more stealth-oriented games like Deus Ex I choose to let the bodies pile up rather than stash them.
-Nick