Can't beat Ninja Gaiden for 360? Try the NES version on the 360! Bryan Livingston and Adam Helps ported Johnathan Turner's SharpNES emulator to run off the XNA Framework. It is over at Google Code as XNA SharpNES and can be downloaded here.
To grab the source code, one needs Subversion (SVN). The project also requires a creators club account which runs $99 a year or $49 for four months to run on your 360. You'll also need the free Visual C# Studio Express and the XNA Game Studio Express.