I've heard about the LifeGem idea and I think it's cool. If it was affordable, I'd probably ask for that.
Ok, this is way out there, but ideally, I'd like to have my body be sent up into space and put into a low orbit. That way when it re-enters the atmosphere, I go out a shooting star.
Or more realistically, I want cremated and my ashes scattered someplace special to me. I think people coming back to "visit" me is creepy. (And my grandpa was a mortician, so I also am creeped out by what they do to your body. Sorry, TMI, I know.)