http://www.radiator.com/ - bought 3 radiators (1 for each Mustang) and they all work great and prices were great.
UPR sells northern alum radiators from their tractor trailer trucks at the park. For 225, you get a nice very thick aluminum 3 core radiator with a billet filler neck for 225. That is the same price as autozones 3 core brass setup. Keep your eye out at the track. my car runs very very cool and have had no complaints.
I run the same one in my 88. It is one heck of a nice radiator, even has all of the mounting slots for the stock fan shroud clips and screws. I have had mine for about 2 years now and never had a problem with it.