Hula hoops were a craze in the 50s. Pet rocks sold like hotcakes in the 1970s. I can't think of anything iconic from the nineties, but maybe those grizzled flannel shirts worn by grunge bands might qualify (though anyone can make a flannel shirt).
Levis Strauss, however, just announced that they have created jeans specially designed for the iPod. I wish the aforementioned article had photos as I'd love to see what they look like, but according to the description, they have a built-in docking cradle for the iPod and retractable headphones.
Now, I'm not saying the Jeans are necessarily a great idea. I question whether I'd want to wear jeans that always have a place for my iPod (currently non-existent, unfortunately). I find it a pain to have my wallet with me everywhere I go, which is why I take it out when I get in the car or sit at my desk. Having an iPod constantly stuck to my body would be no better.
Still, a lot of respondents to a previous post (tic swayback in particular) pointed out that the iPod has built up an ecosystem. It's not a Microsoft-style ecosystem where everything is leveled by common software licensed across multiple hardware devices, but it is an ecosystem. They aren't making special pants for the iRiver music player.
How does one beat that? I could say more, but I'd be more interested in hearing what y'all have to say (I did spend Christmas in Dallas, Texas).