Scott Amron's "Cash Money Clip" is an interesting take on money clips: a dollar bill with a steel plates stuck to it, one over a neodymium disc magnet. I'm a big fan of carrying cash in a clip (I gave up fat wallets in the back pocket and lower-back pain in favor of a small card-wallet and a cash-clip years ago) but I've never really trusted magnetic clips. It's cool to be able to stick teaspoons, small change and bits of metal to your front pocket, but your coins get stuck to 'em and you run the risk of demagnetizing your credit-cards if you absently stick your cash in the same pocket as your card-wallet.
Still, this is just too much fun — and Amron will also sell you a kit so you can convert your own currency to a money clip (you could probably do this without the kit just by shopping around for metal and magnets, too!).
Update: Regarding demagnetizing a card, Ben Laurie sez, "Mythical, apparently. You can't hurt much, even with a rare earth magnet, apart from CRTs.
I've seen this demonstrated with:
a) Credit cards (hotel room keys are a low risk way of trying this yourself).
Apparently to demag a credit card you need an oscillating magnetic source."