Well, since somebody else beat me to the Monty Python “Parrot” sketch, I’ll have to use my OWN brain.
Closed up shop
Is now made of 100% post-consumer material.
Fertilizified.
Became One With The Rainbow. (According to my group)
Came in dead last in the rat race.
Missed the train.
Fruit Salad. (Long story.)
Got sporked.
There are always the “politically correct” ways of saying it:
Cardiovascularly Challenged
Living-impaired
Necro-American
Sub-terrainian plant sustenance provider
BTW, Kilt-wearin’ man, ought we to refer to the deceased as “metabolically challenged” or “differently vital”? 
Sleeps with the fishes.
what are some of those from the movie Patch Adams?
…an exceptionally long blink
Placing a call from the horizontal phone booth.
Well, since Jack Batty mentioned “The Dirt Nap”, all I have left is:
"Bought the harp farm"
Or, as Chuck Yeager and the other test pilots say:
"Augered in."
In an aircraft related theme, when pilots go through cockpit instrument failure they must resort to “POW Mode”. This stands for “Peek Out Window Mode”. If a Captain continues to trust failed instruments and does the final face plant, this is refered to as being:
“Dead right.”
::fade to black::
There are plenty of military terms for it, depending on how it happens. The most common is “getting greased” when one is killed in ground combat. There’s also “fragged” which involves being blown up or killed by shrapnel from other stuff blowing up. Sometimes people who “auger in” (not quite as common a phrase now with the lack of propellers) can also claim to “have his own smoking hole.”
If someone is merely missing in action (MIA for those who don’t already know) lately they’ve been referred to as having “gone Elvis”.
I believe that a better title for these would be EUPHEMISMS for Death.
I really have nothing more to offer here. Mine have all been covered.
(From David Letterman)
Kicked the oxygen habit.