If you are just starting out and don't expect that many transactions per month, you might want to go with Paypal & 2checkout.com, which I've used and never had a problem with.

If you think you will do sales in the volumes of $500 or more, you may want to consider getting your own merchant account. I just signed up with CDCommerce from one of their specials and it was setup within 1 week and they seem to specialize with online (especially hosting) businesses.