If you want to sell your books through your website, you must be able to accept credit cards. Not a website that bumps to Paypal's website and then comes back to you (or not), but one where the buyer stays on your site. Professionalism is key.
One solution is the new Paypal Website Payments Pro. They accept everyone on the planet. I suspect that they will grow exponentially because of that ease.
I am using Authorize.net. While you do have to qualify, it is not particularly difficult a task. One thing that I do recommend is that you go to the list of resellers and check them out. Yes, there is a difference in the percentage that each takes from the sale. I went with MerchantPlus.com because they only take 2.29%. That's less than the others. It took them about 72 hours to authorize the account. Thus far I've been pleased with the results. Also, MerchantPlus doesn't charge a start-up fee (which can be as much as a $100 elsewhere).
What have I been selling? Right now I have a 19-page e-report, The Fifty Cheapest Colleges in America (2004-2005): An E-report on the Low Cost of Education. It is a downloadable product and is only $5. I think the low price has sparked sales. By the way, the credit card fees amount to only 11 cents, so that is a quite good profit margin. Also, and importantly, it is a way to draw people to my website and to get email addresses to send announcements about my forthcoming book.