I've been wondering the same thing recently, I was just waiting for mtgox's merchant services to come online (I think they'll offer what you're looking for) - is walletbit a well-established/trusted operation? It looks good at a glance!
I use WalletBit in a digital downloads shop(no, it doesn't sell much, much less in Bitcoin).
Kris(the owner) made the prestashop plugin i use in the shop responding to a bounty i posted in the forum.
He seems to be a stand up guy and it's the first wallet service i see who is trying to have a decent security, implementing secure cards, just like the banks. Also the part where he paid for users of this forum to translate the site shows me he's serious about expanding his business outside english speaking countries, and that was important to me as most of the customers in my shop don't understand a word of english
Also he is coding other plugins for most opensource shopping cart softwares.
The only downside i see in their service is that people need to have a walletbit account to make payments, but it's also upside for digital downloads shops, as it allows for the downloads without waiting for the bitcoin network confirmations, because the bitcoin is already on the walletbit system.
You should drop by their IRC or give them a call to the numbers they have listed on the website. I'm sure Kris or someone else there will be more than glad to tell you everything you need to know.