There are a number of Payment Gateway options to handle payments online. Finding which one is right for you based on cost-effectiveness and reliability requires some comparative analysis. Some Payment Gateway service providers' websites thankfully provide such a comparison -
Here is Authorize.Net's comparison of Authorize.Net, Paypal & Google Checkout.
If you are targeting an Indian audience, CCAvenue has a comparative analysis of Indian providers.
Some Indian banks offer a payment gateway but the details are not publicly advertised. There does not appear to a consensus on which is good for the Indian e-Commerce market.
What has been your experience?
Related: Integrating PayPal Payments into E-Commerce Applications with ASP.NET