I'm still working on this, and poking around the web today I found the list of all the tombstones in the Simpson's "Treehouse of Terror" episodes:
Tombstones - Simpsons Wiki
They're actually not as funny as I would have hoped, but they are the "length" I'm looking for, if that makes sense.
I like the "Grateful Dead" tombstone when next to an "Ungrateful Dead" one with some bones crawling out of the "ungrateful" one, otherwise I'm still searching for about 4 more...
Some other links to tombstone jokes in media:
http://tvtropes.org/pmwiki/pmwiki.php/Main/GraveHumor