Paypal is one of the easiest and cheapest ways for small business to accept credit card payments. There are two methods of using Paypal:

• Paypal Standard - Paypal standard is the easiest cheapest way to do business with Paypal.  In addition, it gives you the benifit that no credit card information or processing is down directly on your site.  This is nice from the perspective of delegating security and risk, however it also does force your users to leave your site in order to make payment. 
• Paypal Pro - Payapl Pro allows you to use paypal like a merchant account.  This way the user never leaves your site which has obvious benifits to you and the customer.  However, using this method is a little more expensive and also requires your shopping cart software to have "express checkout" functionality.  Currently one of our favorite commerce packages zen cart does not support Paypal Pro (more info).  A list of approved carts can be found on the paypal website.