Is there a production grade SimpleDB library, preferable built in C#. If not, May I use the VB.NET library on a C# project as a reference?
Amazon provides a C# version of their SimpleDB library at http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1133
But also: assuming you have Visual Studio or at least the .NET Framework SDK, you could compile Amazon's SimpleDB library as a DLL, then include the file and reference it in your C# project and that would work pretty much the same way.
Here you will find a C# SimpleDB library
There's also an open source SimpleDB provider, which you can find here, which might come in handy.
Check out Mindscape's LightSpeed that supports SimpleDB ORM out of the box. They have a beta product called SimpleDB Management Tools for $29 USD that is in beta, but these guys produce great software so my suggestion would be to investigate and feedback to them.
The plus side is you get a great ORM for other uses.
Amazon just recently released the AWS SDK for .NET. It's a step up from their prior offerings as far as I've seen (though I'm admittedly very new to the AWS thus far.)
Check out Stratosphere. It's open source, C#, Mono compatible library for SimpleDB, SQS and S3. Supports latest conditional updates and consistent reads. Includes local implementation based on SQLite that closely mimics SimpleDB for unit testing etc. Also has local file system implementations for S3 and SQS APIs. Additional download contains command line utility for managing SimpleDB, SQS and S3.
You may want to check out Simple Savant, an open-source .NET persistence library designed specifically for SimpleDB (I'm the creator). The first release was nearly 2 years ago, and it's in use by quite a few beta and production applications. I keep a partial list of the applications I know about here.
For a commercially supported solution, check out the /n software Amazon Integrator - http://www.nsoftware.com/ibiz/amazon. Includes components for .NET, as well as Java, C++, COM, Delphi etc.