This freeware Visual Studio 2003 add-in provides a multi-language spell checker for your comments and string literals. Without setting any options it knows how to spell check C#, VB.NET, C++.NET, J#, C/C++, HTML, XML, Java, and other text-based files. It works on the selected code or on the entire current file or project, and has many other options. Version 2 fully works with ASP.NET and Web Services projects.
You are only required to have MS-Word 2000 or higher because this add-ins needs the objects they expose.
[Via Anders Norås' blog ]