Are there any good libraries for accessing GRIB2 data in .Net? Specifically, I want to be able to quickly pull subsets of weather data from a grib2 file based on time and location.
GribApi.NET is now freely available. It supports reading and writing GRIB 1 and 2 files.
Disclosure: I am the author of the C# wrapper.
With FWTools there are .NET wrappers for the GDAL, which can read .GRB (GRIB2) files.
GribCS gives fine grained access to grib files. Using GDAL you might be loosing some interesting information.
I have no experience with .NET, but the standard c library for accessing grib2 files is g2clib. You could call the functions of that dll. I think it is better than using gdal, because you are more likely to cover every aspect of the grib2 definition.