OCZ, the California-based memory specialist, might have the answer - 8GB and 16GB upgrade kits!
Before you whip out your wallet and hit your favorite online parts retailer, a couple of words of warning. First, you can’t just slam these modules into any system, because these modules have a density of 4GB. Before you can use these modules you’ll first need a system that’s equipped with either a P43 or P45 chipsets motherboard (such as the ASUS P5Q WS or the Gigabyte GA-EP45-DS4P). In addition to this, if you want to use the 4×4GB upgrade kit (as opposed to the 2×4GB kit) to go up to 16GB of RAM the motherboard HAS to be rated to take 16GB of RAM, something which not all P43 or P45 chipsets boards are rated to do (for example, a quick look through the specs show that the DFI LANPARTY DK P45-T2RS and the ASUS P5Q Pro only support 8GB of RAM).
Source:→ ZDNet Hardware 2.0 Blog