Best GPUs avaiable for OpenCL on Mac?

I am starting the long journey of writing OpenCL implementations of my Lab's in-house image correlation programs. We [the lab] is currently based on PCs, I am however on a personal Mac. I am looking for details on the what the best GPUs available are for the Mac. I am reading lots of wonderful things about the new Fermi cards, but I haven't seen much when it comes to Mac compatibility. Thanks!