There are a number of online businesses that will process credit card transaction for you as well as fulfilling the order through a digital delivery system. You upload your digital product to their website and they deliver it for you. THis saves you having to open a merchant account which can be expensive in some parts of the world.
ClickBank
ClickBank runs a large affiliate program. Producers of list their products along with useful sales information, a commission payout that ranges from 10% to 100%. A vast network of potential affiliates can then browse these listings and choose which products they wish promote to their distribution lists and website clients. All sales and transactions are handles by Clickbank who take their cut and distribute commissions.
PayDotCom is a good alternative to ClickBank. You do need a PayPal account but you can list your first product for free and any subsequent products at a very low cost.
DigiBuy processes credit cards orders for you so you do not need your own merchant account. It also delivers your products through a download link. They send purchasers a password in an email which they can use to access the download for a limited period of time. The service is good, but more expensive than most sites of this kind.
Kagi provides an e-commerce portal that sells 1,000's of digital products and hard products wqorldwide. They offer a complete delivery system for digital products, as well as an affiliate program. You do not need a merchant account.