I'll third BMT. I haven't seen what they're like personally as a developer, but they've always been great on the affiliate side and that's not too common in the industry. I'd definitely use them if I was going to produce something for affiliate websites (Aldorlea, amaranthia, etc).
I'll also second the "Nah" for Plimus/Bluesnap. Here's a
quick article I found. I can't confirm if it's accurate, stopped using them before it was posted.
Another option for your own website is the Humble Bundle Store. They're very trusted by game purchasers, while a custom-looking store might not be. You can read a bit more about it
here.
You'll want to make sure people can actually download their games later while shopping around. Many of the payment providers only let people download them for ~90 days and charge your customers a "download insurance" that allows them access for another year or two.