If you can find it, Evelyne Beers' "Time Passes" is my favorite.
My two second picks are "Fiddler's Green" and "Parting Glass."
Knowing my friends, they'll be singing "Look at the Coffin" (aka "Bloody Well Dead") at my wake, so I might as well request it.
But to go out on an up note, nothing beats "Saints Go Marching In"!