I went with Photocart . Most of the Pros that I know, were using it at the time...I assume they still are.
It's an application that is loaded/hosted right on your own website. I like this because you don't have to send your clients away from your site and you have full control over it.
It's not really a cheap purchase, but it's a one time purchase. After that, there are no costs. The software is updated occasionally, for free.
The one down side is that (as far as I know), there is no order fulfillment option. In other words, you (or someone) still has to look at any orders, then send the images to be printed and get them to the client. This is usually fine if you're not super busy, but for a photographer who is busy, this could be time that would be better spent behind the camera. In that case, it may make a lot of sense to use a service that will print and ship photos directly to your clients (but that will cost you a commission fee).
I should also mention that it's well known that in-person proofing & ordering is way, way more successful
When I have to do on-line proofing (I prefer in-person proofing MUCH more) I simply create a password-protected directory on my website and upload a Lightroom gallery to it.