Hi Hi! I'm a photographer and for client viewing I use www.instaproofs.com
its FREE!!! and you can have watermarks placed across your images. You set your own prices and if/when they do order.. instaproofs sends you the order and then the payment from them . they deduct a small fee only when they order. You then are given the freedom to order from ANY printing company you choose. I LOVE this because I am able to order through WHCC.com whom I love and adore..
Also.. for my images that I upload for viewing I resize them at 72dpi.. this way if they do manage to take them.. they wont be able to print them because they are only large enough for viewing on a computer.