dotNetRDF is a .Net Class Library for working with RDF and SPARQL programatically built with C# 3 for the .Net Framework 3.5/4.0/Silverlight 4 and WIndows Phone 7. It provides a simple object model for representing RDF, SPARQL Queries and Updates and understands all common RDF and SPARQL syntaxes.
Extensive documentation is available on the website and support is available via the mailing lists.