Someone internally here alerted me to this neat little utility that makes looking for duplicate spn's a breeze. If you are looking for a quick tool to help with it this is a great one.
http://www.pluralsight.com/blogs/keith/archive/2005/10/12/15503.aspx
They even share the code with you so you can take it and expand it.
http://www.pluralsight.com/keith/samples/DumpSPN.zip