In order to accept credit card information directly on your site, you need to be PCI compliant. This involves paperwork, and once you have significant volume, audits.
WePay provides a simple checkout API that you can embed on your own site via iframe. This way you can have the entire checkout process on your own site (unlike most PayPal APIs), but without dealing with the PCI nightmare. http://stage.wepay.com/developer
You can also use stripe, which provides a JS solution where the client sends CC details to the stripe server, which is PCI compliment, and you receive a token you can use on your server. The CC numbers never touch your server.
there are some other javascript payment solutions I think, but the stripe one is the best I've seen.
WePay provides a simple checkout API that you can embed on your own site via iframe. This way you can have the entire checkout process on your own site (unlike most PayPal APIs), but without dealing with the PCI nightmare. http://stage.wepay.com/developer