Maxima radiator from Radiators.com about a month ago. They sold me a Koyo with a lifetime warranty for $132.00 shipped to my door. It is quite a bit bigger than the stock NA one, but everything fit perfectly. I can't comment on performance though, seeing as how my Z has been in the body shop ever since I installed it. I think I'll be very happy with it. Only thing that worries me is the fact that it still has the problematic plastic connectors(the lifetime warranty covers that though). I also replaced the temp sensor and aux fan switch when I installed the new radiator. If I ever get my Z back, I'll see what the performance differences are.
My NA 2+2 may never be as fast as a Twin Turbo, but I sure look cool when I'm picking up my groceries.