If you really want to get your freak on with this, check your motherboard for compatibility first. It seems Corsair is going to be launching a 16GB DDR2 800 MHz memory kit.
The Kit will have four 4GB modules and is tagged under SKU code QUAD2X16GB-6400 already. You might want to save up some hard core cash though, according to kokatu the price is going to be 83.000 Yen ... roughly 850 USD.
Well, it is high density 16 GB of memory of course.