Be witty, be pithy, be either nice or scathing, and rhyme if you want. Rhymes in epitaphs can add a bit of zing, but you can have just as much zing without it.
#1:
Here lies Mr Elvis Presale
He was told that he had email
(He didn't want to read one word
From buyers whom he'd gi'en the bird)
Alas! If only he had read
The death-threat - then he'd not be dead.
