The dollar is not going to be giving up the ghost as the world's currency any time soon. Too many billions of them are ferreted away in boxes in gardens and into mattress ticking and under armed guard around the globe: Ulysses S. Grant's face on a $50, Andrew Jackson's on a $20, even the un-president Ben Franklin on the $100. Maybe there are still a few out-of-print $500 William McKinleys moldering out there behind some wallboard somewhere.
But if the day comes that we do convert to a new global currency, here is how we bypass all the rancor and nationalism and factionalism. We embrace a currency that already exists, one that is recognizable and beloved around the world, one that is virtually devoid of political and ideological content:
Harry Potter's. The money of magic. Golden Galleons, silver Sickles and bronze Knuts.
Of course the world can't operate on an actual gold standard like Potter's magical banking world; the currency, like currency now, would represent values, not hold them. But hundreds of millions of children have grown up reading the books and knowing these currencies, so it would be easy to adopt and embrace.
(One fansite puts the value of a Galleon at nearly $10, and a knut at about two cents American. There are, unsurprisingly, several websites that helpfully convert Potter money into real-world currencies.)
Harry Potter's world also trades in leprechaun gold, counterfeits which look and feel like the real thing, except they vanish shortly after they change hands. If only we required any potentially flighty financial dealings to treat money like leprechaun gold until it's proven to be worth the real thing, we might have been able to tell bad money from good, avoided the Madoffs and AIGs of this world, and wouldn't be in the pickle we're in now.
At this point, the goblins of Gringotts bank look a lot more trustworthy than the gnomes of Zurich.