If you don't want to integrate with a 3rd party bitcoin payment provider you can implement your own payment module for Bitcoin (but also for Litecoin and every Bitcoin-derived altcoin) very easily with BitcoinLib that is written in C#.

Some of BitcoinLib's features:

• Fully compatible and up-to-date with Bitcoin 0.9.1 RPC API.
• Design-by-contract, service-oriented architecture.
• Strongly-typed structures for complex RPC requests and responses.
• Implicit JSON casting for all RPC messages.
• Extended methods for every-day scenarios where the built-in methods fall short.
• Exposure of all RPC API's functionality as well as the extended methods through a single interface.
• Fallback mechanism for timed-out RPC requests.
• Custom RPC exceptions.
• Supports all Bitcoin clones.
• Can operate on unlimited daemons with a single library reference.
• Litecoin integration included.
• Each coin instance can be fully parametrized at run-time and implement its own constants.
• Console test client with demo methods implemented in it.
• Disconnected raw RPC connector included for quick'n'dirty debugging.
• Testnet ready.
• Fully configurable.

If you are new to bitcoin, just for accepting payments it is recommended to use a service like BitPay or BIPS

They will provide

• Easy API - as opposite of bitcoind API which is intended for low level bitcoin tasks. If you are familiar with PayPal moving to other payment providers should be easy.

• Fiat to bitcoin currency and vice versa

• Address generation and matching orders to their bitcoin payments

Working with bitcoind directly from a web developer perspective is a little cumbersome, so I don't recommend it if you lack bitcoin experience.

You can use open source bitcoin/altcoin package from gourl.io:

https://github.com/cryptoapi/Bitcoin-Payment-Gateway-ASP.NET

It works fine in my project.