The refrigerant of choice that does not deplete ozone for manufacturers that manufacture residential systems is R410. The trademark for this refrigerant under the Carrier and Bryant brand names is Puron.
In our experience, first cost for systems that use Puron are not much more costly than systems that use the present ozone depleting freon R22.
A production cap was implemented on R22 in 1996. In 2004, that production cap will be reduced 23% below the 1997 consumption. This makes people believe this will cause a shortage of R22 and a significant increase in price. This is what happened to R12, which the production was banned in 1996, the price actually jumped from $80 per pound in 1990 to $600 in 1997. After January 1st, 2010 equipment can no longer be manufactured using R22.
The safe bet is to buy a system with R410/Puron. Not only does it protect the ozone and the environment but probably will also protect you from escalating refrigerant cost in the future.