Hi. After asking this question myself a few months back (search former threads on this) we settled on the IQAir Health Pro Plus. It has a hepa filter and carbon filter, and does not have ozone (which is bad for cf lungs). It is fairly expensive ($850 for a unit that is supposed to clean 2000 square feet..i think).
Also, you want one that really takes out the fine particulates, which filters up to either .03 or .3 microns (again, can't remember the exact number here, but not all filters filter out these really small particulates, so ask when you are deciding).
They also have a whole house filter, which I believe is about $4K, but it doesn't filter out these smaller particulates.
Edan.