We use Worldpay.com but there is Authorize.net - they both work with a great backup service. It's not just the merchant you want to worry about there is also the software, don't pay a monthly fee it's not worth it. We use Jshop to sell ink cartridges (see our site www.theinkmarket.co.uk) but are moving over to X-cart because you can up date on line and it give you loads more features such as gift vouchers, stats, discounts etc. it cost only $195 (dollers) installed. We have yet to use it but seems excellent.