I know one that uses JSONRPC would be best but there is alot of people that would like to start a bitcoin business but just cant afford to pay for a vps/dedi to host it. The ewallet services are unreliable but a necessity.
If so you might as well host your site on shared hosting run by a shared-bitcoind provider whose shopping-cart interface interfaces to the shared bitcoind. At least such a service might be run by someone who put some work into it, such as actually implementing a shareable bitcoind and a shopping cart interface that interfaces with it. That way you could hope for a little longer grace time before the sheer number even of tiny wallets of very cautious merchants adds up to enough coin they'd figure they have paid off their initial investment and made enough profit to fly by night with all the coins...
But hey, what kind of business is the site going to run? Whatever it is could be added to the control panel as one of the applications you can have auto-installed for you, like shopping cart, forum, hosting reseller, drop-shipper-affiliate or whatever you have in mind...
-MarkM-
P.S. Amazon Affiliate could be a good one, we could hack whichever of the "instant Amazon superstore" scripts beat all the others from way back when in usefulness power functionality etc to accept bitcoins to the wallet and pay Amazon with Amazon points or something maybe, or even just let people pay with Aamzon points or credit card or anything they want, what do we care, we get commission regardless...