ASUS M4A89GTD PRO HELP! Best DDR3 Memory

Hello Experts,I've been researching DDR3 memory for days and I am thoroughly confused This is my first build and I need all the help I can get with selecting the right & best DDR3 memory.Which is better 2x4 or 4x2? My build is ASUS M4a89GTD Pro, HAF 932 case, Cooler Master Silent Pro Gold Rs800 watt psu, XFX Radeon HD 5770, Phenom 2 BE x2 550 wfk2dgi, Windows 7 Home Premium 64 bit. I dont have hard drives or memory yet but, thinking of getting WD velociraptor 150gb or 300gb sata 3.0 gb/s or sata 6.0 gb/s for OS and a WD Caviar Black WD1002FAEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" for other media. I will be upgrading to a AMD Phenom II X6 1090T Black Edition Thuban 3.2GHz 6 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Six-Core in the future. I would appreciate any and all comments..Thank you