An excellent place to start is Wired magazine's recent article on the Future of Money:
The New Ways
Type a friend’s Twitter handle, a dollar amount, and twitpay to transfer funds to their PayPal account.
Instead of entering credit card information anew for every online purchase, users fill in their phone number and the charge shows up on their monthly bill.
The latest from Twitter cofounder Jack Dorsey, this 3/4-inch cube turns any iPhone into a credit card reader.
This mobile app uses PayPal to enable charities to accept small donations without the usual exorbitant credit card transaction fees.
Travelers can avoid the hassle and fees of swapping dollars for euros by transacting in virtual currency in this international network of workstations.