Jon Morisi has a script to find orphaned users:
With the SQL Server 2005 end date approaching, you may find yourself migrating databases. One of the gotchas with any database migration is orphaned users. Below is a script I put together, and have been using for years, to help me resolve issues with orphaned users:
I’m not a fan of the sp_msforeachdb in there because there are issues which can cause “each” database to skip databases. If you have installation authority, Aaron Bertrand’s sp_foreachdb is a better alternative, and if you need to do Insert/Exec calls, there’s a newer version which removes the INSERT/EXEC in that procedure.