What ki d of memory?

Trying to increase my memory. I only have 2G and I want to have 4. Maybe more I dont know. Play a lot of games.
Someone suggested the Mushin Enhanced Blackline 2gb 240 pin ddr2 sdram 1066(pc2 8500)

Any other suggestions will be appreciated. Ohh, I have already uo graded my vid card.
Here is my system config:

System Configuration:
Case: Digital Storm Twister PRO (Black Anodized Aluminum Finish)
Power Supply: 750W Thermaltake (SLI Compatible) (Silent Toughpower Edition)
Processor: Intel Core 2 Quad Q6600 2.4GHz (1066MHz FSB) (8MB Cache)
Motherboard: nVidia 680i LT Core 2 Quad (By: eVGA) (nForce 680i SLI)
Memory: 2GB DDR2 Corsair at 1066MHz Dominator (Dual Channel) (Extreme-Performance)
Floppy / Media: Digital Media Card Reader (Black)
Hard Drive 1: 500GB (Western Digital / Seagate) (16MB Cache) (7200 RPM) (SATA)
Hard Drive 2: - No Thanks
Raid Option: - No Thanks
Optical Drive 1: DVD-ROM/CD-ROM (DVD Reader 16x / CD Reader 40x)
Optical Drive 2: DVD±R/RW/CD-R/RW (DVD Writer 20x / CD-Writer 48x)
Network Card: High Speed Network Port (Supports High-Speed Cable / DSL / Network Connections)
Modem: - No Thanks
Video Card: nVidia GeForce 8800GTS 640MB (By: eVGA / Asus) (PCI-Express)
TV Tuner: - No Thanks
Sound Card: Motherboard Multi-Channel High Definition Audio (7.1 Channel)
Physics Card: - No Thanks
Cooling: Air Cooled Stage 3 (Silent Artic Cooling (TwisterBoost Overclocked)
Case Lighting: - No Thanks
Round Cables: - No Thanks
User Manual: Personalized Platinum Digital Storm Binder (Includes Paperwork/Benchmarks/CDs/Manuals)
Windows OS: Microsoft Windows Vista Home Premium
Restore Kit: Digital Storm Specialized Recovery System (DVD Image Based)
Protection: - No Thanks
Office: - No Thanks
LCD Display: Samsung 24 inch (Widescreen) (Black) (High-Performance Gaming Display)
Surge Shield: - No Thanks
Speakers: Logitech 2.1 System (Black Edition) (Model R20) (Includes Subwoofer)
Keyboard: Logitech Bluetooth MX5000 (MX 5000 Keyboard + MX 1000 Laser Mouse)
Mouse: - No Thanks my keyboard comes with a mouse
Warranty: 3 Year Platinum Care Extended Parts & Labor Warranty
Support: Lifetime Toll-Free Platinum Care Technical Support