Yeah, this is sort of bummer topic for the first full day of summer, but since The Great Beyond is an inevitability for most of us (and I say "most" because I'm sure that the rich will achieve The Singularity in our lifetimes), it's best to be prepared.
My wife and I do have a will--everyone should--but we never specified anything about last songs for any kind of funeral or memorial service. But if you talk to my friend Phil the Funeral Director, he'll tell you that many people make this sort of provision. AC/DC is popular, apparently.
Frankly, though, I'm stumped.
The AV Club polled some people on their staff and came up with an interesting selection. My favourite pick is this one from the sound track of the 1974 Brian De Palma film, Phantom of the Paradise, which plays over the closing credits.
Assuming you want a final song of some sort--and I'm not convinced that it's necessary--what would you like your send-off theme to be?