I was looking around and saw a card called a Radeon X800XT Mac Edition, it is the only card that actually uses GDDR3 ram(or at least the only card I have seen). My question is, is it a good card? It seems like these cards are a bit expensive.
It is a fantastic card! I personally prefer ATI cards due to their generally stellar support in OS X.
They are outstanding for pretty much any PPC Mac. Two concerns are power and heat. These cards require an additional connection to the power supply so a marginal power supply may struggle to provide power. Also, these suckers put out a lot of heat, so you may need to take special measures to dissipate the heat so you can avoid crashes and freezes.