Serious:
"I never wanted to know what was out there more, then right now." or "My curiosity for the future has finally peaked." and I would have the notes to "Walking in the Air" from "The Snowman" etched across the tombstone.
Silly:
"High Score: Over 9,000!" from "DBZ" and Pinball machines
"Everything floats down here Georgie!" from "IT"
"Told you it wasn't going to work!"
"I survived life!"
"Can you hear me knocking?"
"Lay down so I can get a better look at you..."
"The boss sent me here."
"Pushing up daisies isn't as hard as they said it would be."
"Finally, a job that I'm good at!"
"Keep it down up there, don't make me come up there!"
"Why do I need a suit and tie for this?"
"The grass far less greener on this side of it..."
"I got no bars down here. Screw AT&T!"
"Help! I'm stuck in a tombstone factory!" from Llil a poster above me ^ ^ (I really liked this one)