paypal.com

If you've ever bought or sold anything online, there's a good chance you've used PayPal. Unless you're Lindsey Dowd, you probably agree that it's a smart way to do transactions, as you can syncronize your bank accounts and have people pay you via Credit Card. The website is organized well, and has good customer service, as I had to deal with a fraudulent Nigerian customer this morning (but that's another story).