.NET Spatial Reference and Projection Engine

Proj.NET performs point-to-point coordinate conversions between geodetic coordinate systems for use in fx. Geographic Information Systems (GIS) or GPS applications. The spatial reference model used adheres to the Simple Features specification.
Supports:
    * Datum transformations
    * Geographic, Geocentric, and Projected coordinate systems
    * Compatible with both Microsoft .NET 2.0, Mono, .NET Compact Framework & Silverlight
    * Converts coordinate systems to/from Well-Known Text (WKT) and to XML
Projection types currently supported:
    * Mercator
    * Transverse Mercator
    * Albers
    * Lambert Conformal

Go to http://www.codeplex.com/ProjNET

See also these related projects.