My parents got one of these whole home IQAir air purifiers installed in their house. I like IQAir’s room air purifiers too, e.g. the HealthPro Plus — looks like it’s won some awards and both the whole house and in-room purifiers are probably worth a look if you’ve got health issues. I guess these are what they’ve been installing in homes for the Extreme Makeover Home Edition shows.
I like radiant heating systems the best (which we don’t have and don’t plan on doing for our house) because they’re the most efficient and provide the best type of heat, but it doesn’t help when it’s hot and you need an air conditioner. For most people, forced air heating and cooling system is best and might as well check out the IQAir purifier while you’re at it.