OpenCover
Code coverage tool for .NET 2 and above
OpenCover is a free and open source code coverage tool for .NET 2 and above (Windows OSs only - no MONO), with support for 32 and 64 processes and covers both branch and sequence points. It uses the profiler API that is currently only available to .NET Frameworks running on the Windows platform.
OpenCover is an attempt at building a code coverage utility that addresses certain issues in maintaining PartCover support for 64-bit processes.