.Net DNA/Codon Parser
I don't know much (read: anything) about the .NET framework but a little search turned up Microsoft's .NET Bio:


  .NET Bio (formerly Microsoft Biology Foundation [MBF]) is a language-neutral bioinformatics toolkit built as an extension to the Microsoft .NET Framework—initially aimed at the area of Genomics research. Currently, it implements a range of parsers for common bioinformatics file formats; a range of algorithms for manipulating DNA, RNA, and protein sequences; and a set of connectors to biological web services such as NCBI BLAST.


Free (as in beer) and open source!  And from this it looks pretty cool.