Here's a list of the things that Apple will and won't let you get engraved on an iPod.

Here's some favorites of mine, first off, things you can't have engraved:

10,000 Stolen Tunes Inside
Not to be used as a suppository
Lick My Shiny Metal Ass
Something small & white that Enrique Eglasias Isn't In
Steal this? Will self destruct when used
Screwing The RIAA One Download At A Time

And now for some funny ones that were accepted:

This engraving has lowered my resale value
To all the Chinese children who made my iPod, Thanks!
Me vs. RIAA: Exhibit A
98% Liberace-free
Your mamma uses a walkman.

and my favorite...

CDs are for amish people!

[Thanks to FSJ for the point]