I've always disliked the currency of the United States. Apart from the spooky one dollar bill, our money looks dull verging on ugly, and it's only getting worse. No one will accept the presidential $1 coins as change because they look like a crappy cheap token. We always have to take a stack to the bank.
One day though, the dollar will stop it's long and far decline, and the people will need something to reassure them that they can have faith in their money again. I think the best way to do that (apart from having a fiscally responsible government that has cast the Fed out into the wilderness) is to have currency that speaks power, wisdom, and confidence. Best way is to look to the past for inspiration, and the best example of all is the 1896 silver certificates known as the "Educational Series".
The fiver. Best of the lot.
Ah, the good old days. Half naked deities bringing electricity to America so it can be even more awesome. The rumor is that the notes were short lived because of prudishness over the overexposed goddess, but today the uproar would be over the theme of the $2 certificate, an allegory titled "Science Presenting Steam and Electricity to Commerce and Manufacture". Commerce? On money? Helped by Science? Outrageous!