Internet shopping is great, but most of it is off-limits if you don't have a credit or debit card. Unless you thrive on gift cards, you'll have to settle for whatever is in physical shops. Today, though, Amazon is removing that barrier. It's launching an Amazon Cash service that lets you apply cash toward your online account. It's a bit convoluted -- you have to visit a participating store, show a barcode (either on your phone or on paper) and fork over your money. There are no fees, however, and you can contribute between $15 to $500 at a time.