Build a board of advisors of three year olds and email valleywag. Make firebreathers wear tshirts to show how hot your start up is. Create disposable tattoo which doubles up as an invite code when put under the shower.
Email me for pointers, i love this sort of stuff.
Iron-on tattoos. Water-based temporary tattoos have been done. Iron-on ones would guarantee some sort of press coverage!
Seriously, though, wouldn't it depend on the nature of the audience you're trying to attract? Three-year-olds would be great for a preschool games site but not so good for, perhaps, helicopter pilots. Can you be more specific about your startup?
To oversimplify the ideas in his book, Godin says that the old methods of marketing are essentially dead. The only way to market efficiently is to build compelling ideas directly into the product rather than saving the innovation for the advertising.
In addition, I'd recommend reading "The Tipping Point" by Malcolm Gladwell. It's a stimulating, accessible book that presents the fundamentals of how ideas spread through a populace. Pay close attention to the idea of stickiness and see what you can do to ensure that your product is sufficiently sticky.