If you think that 4GB of memory just isn't enough for memory-hungry Windows Vista and Crysis, or if you use your computer as a professional workstation, you might consider OCZ's new 8GB "quad kit."
The new kit goes under the name of OCZ DDR2 PC2-6400 8GB Platinum Quad Kit. It works at 800MHz with 5-4-4-18 latencies. As with the rest of the Platinum series, these modules also use Platinum mirrored XTC heatspreaders for cooling. The new kit operates at 2.1V with extended Voltage protection to 2.2V. The new 8GB quad kit also comes with OCZ's lifetime warranty.
Since DDR2 prices are hitting the floor these days, this sounds like a good upgrade solution. Just for reference, you can get the OCZ 4GB Platinum kit with similar specs for as little as €109.80 in Europe. It looks like OCZ is keeping its eye on the market.
You can check out additional info at OCZ's product page.