After several weeks of trying all the various e-marketing software (DL Guard, Quick Sales, etc.) I finally stumbled upon E-junkie. It is by far the easiest one that I tried. By Far! It took me less than 15 minutes to set it up on my WordPress site, do a test purchase, and get paid. Delivery of my product to the "buyer" (my girlfriend) was instantaneous - and they even handled the confirmation email.
ZERO installation. Seriously. You need only paste an HTML code on your site to get the appropriate "buy" button - as well as shopping cart etc. No C-Panel gymnastics, no worries about using the wrong link to your product, etc. AND - 24hr. customer service with and honest to goodness phone number!
If you're just starting-out and looking for the simplest buying solution available - this is it. FYI.