What it is: Google Wallet makes it easy to pay--not just online, but in stores too--and it works with any debit or credit card.
Why it's useful: Paying is made not only seamless: it's so mobile-friendly that you can make payments while you're waiting in line.
Pro tip: Owe a colleague money for dinner last night? In Gmail, there's a new-ish "attach money" icon that will let you send money quickly and easily using Google Wallet.