I've thought about this quite a bit.
Plane crash by a major airline carrier.
Reasons:
1) Great view
2) Likely to be a quick death
3) A moment to grasp what is about to happen and make peace
4) Hopefully with someone you care about
5) Your family will get plenty of money out of the settlement so you don't need to worry about your family being provided for.
6) You may even have a chance to call a loved one and leave a good bye voicemail or write a note and put it in some sort of item like an aluminum water bottle.
But really, peacefully in my sleep.