Disposable credit card numbers: Why share your 16-digit number with online merchants, particularly those you've never heard of? Many major banks let you create a unique, temporary card number for each online purchase.

For instance, is a free service for Bank of America Visa and MasterCard holders who bank online with the financial giant. When you want to make a purchase online, you open a new browser window and sign in to your Bank of America account. Next, you follow the ShopSafe instructions to create a 16-digit credit card number, which you use on the vendor's site in lieu of your regular number. (The vendor won't know the difference.) The temporary number has its own expiration date and security code, and is valid at only one online vendor. You may reuse the number when you buy from that vendor again, however. Other institutions, including and , have similar services.

Even if you don't use a disposable number, you're protected from unauthorized credit card purchases. If someone uses your card without your permission, your liability typically ends at the first $50, according to the . And many card issuers now have zero-liability policies, where you won't have to pay a penny.

Online payment services: If you would rather not fuss with lengthy credit card numbers, expiration dates, and security codes, an online payment service is a handy alternative. The free service stores your credit card details and doesn't share your full card number with merchants. If a vendor accepts Google's payment service, you can make a purchase simply by clicking the Google Checkout button on its site. Naturally, you'll have to sign in to your Google account to complete a transaction. The venerable is another option, and it won't charge you a fee to buy stuff online. Both sites will reimburse any unauthorized purchases in full, as long as you report the fraud within 60 days.

Prepaid credit cards: Personal finances shaky? Can't obtain a regular credit card? You still have online-shopping options, albeit pricey ones. Usually you can get a without a credit card or bank account.