Can I produce a list of only unique contractors we have used on certain jobs?

I would like a unique list of contractors we have used on certain jobs.  I don't want the list to be populated with several of the same contractors.  In other words, we have used ABC company on 50 XYZ-owned jobs, but I only need ABC listed once.  Is there a way to produce a lookup with unique names only?  ie  ABC on XYZ, JKL on XYZ, DEF on XYZ, ABC on 123, ABC on 678, etc.