Amer Gerzic created a great plug-in to format source code while writing a post in Windows Live Writer.
You simply paste the code into the plug-in Window, specify the appearance of the code snippet.
He supports a wide range of languages within this plug-in which makes it so interesting. Currently supported languages are ASPX, C, C#, C++, COBOL, Cold Fusion, CSS, Eiffel, Fortran, Haskell, Java, JavaScript, JScript, Mercury, MSIL, Pascal, Perl, PHP, Python, Ruby, SQL, Visual Basic, Visual Basic Script, XML.