While all these bus ticket selling sites offers you facility to buy through credit card and debit card , some of these also provides to deliver the bus tickets on a small fee like Rs 20-25 to your home.
Clicking http://bus-tickets.rediff.com/index.php will take you a simple window like below
The rediff bus search is all India bus search and shows all kinds of state bus services available. The bus tickets can be booked from there itself.
This site also provides a very simple interface to search for the bus . However the bus search is based on Volvo type which are much better . Clicking http://www.ticketvala.com/ will take you to following window
One of the important feature is that you can choose even the seats available , just like you choose the seats while making web-check in of airlines.
This is bus ticket booking site primarily catering to bus services of major tourist spots. Click http://www.redbus.in/index.aspx and you will be taken to window below
They can deliver you the bus tickets even to home in some select cities. The bus search and booking is mainly catering to southern and western part of the country and some other major tourist spots.
This site is also providing the facility for online booking of bus seats in major towns. Click http://www.abhibus.com/index.php and you will be taken to following window