For the record, just because this is strictly creative does not mean it will be gentle or nice for the person about to be broken up with.

• Spell it out on a pizza with M&Ms
• Shave it in a hairy person's back
• In the sky!
  • Banners
  • Smoke
  • Giant blimp
• Do it on national television [that would suck for the person, though, and who knows, another internet meme bigger than Kanye's "Imma Let You Finish" might surface overnight]
• Become famous, write a song, and "dedicate" it to them
• Billboards, anyone?
• Post it on MLIA or FML and give them the link to read it
• Shout it through a megaphone at a stadium
• Scrolling marquee glasses; wear it around them
• Write the words in shaving cream on their mirrors
• Get them to go on a scavenger hunt and with every object they find, explain bits and pieces of why you're breaking up with them