Done for you shopping carts.
Actually "done for you" shopping carts can be a great idea. So long as your budget can stretch to them. But always look at the cost if you have to upgrade. Usually they have a payment tier where it starts low but the payments get much larger as your needs grow. Although having said that, if you are turning over a million dollars a year - paying a thousand a year for the shopping cart is not such a big deal. And they handle all the security, hosting, upkeep, etc, etc.
There are a few to choose from but I've heard good things about Shopify (but I haven't used them myself).
Cheers - Ingenyes.