There are many options but I have always loved JM Lab with older Mc equipment. You don't mention a budget but I would recommend the Electra 906 monitor as a synergistic candidate.
Thanks Arthur and Rich. I'll give the 906's and Classic 3's an audition. I've also read in other threads that I should try Paradigm's and Klipsh. I think these will give me a good start.
Arthur, as for budget I don't have a specific budget (that can get scary!) but I guess I could find something to complement the 4100 for $500-$800 used. If something really knocked my socks off but cost more I'd probably amortize it in my mind and pay a good bit more. :-)