Clover.NET provides code coverage for .NET projects. Measures method, statement and branch coverage. reports in XML, HTML or via Visual Studio Plugin. A suite of NAnt tasks are provided. [Free for Open Source and Non-commercial projects] http://www.cenqua.com/clover.net/
Object-relational mapping and code generation tool for C# generates 100% of the data access code. Auto generate wrappers for stored procuedures. http://www.olero.com/OrmWeb/
A series of advanced collections and more than 50 generic algorithms that are designed to complement, not replace, the basic features found in the .NET Framework. [Commercial] http://www.recursionsw.com/c_sharp.htm
Free open-source plugin for Eclipse (itself a free and open-source development environment) with syntax highlighting, content assistant (intellisense for C# keywords), and ability to compile code from within the IDE. http://www.improve-technologies.com/alpha/esharp/