OP your build looks decent. To get most gaming experience from your system, you'd probably spend 1:2 on CPU vs video card. SLI/Crossfire is a personal choice and I totally agree with Mucat. When I built my system last Nov, I chose to go single card because of heat/noise and other considerations.
SSD will boost your game/windows loading immensely but won't help with fps, so you can upgrade that later on if your budget is limited. Sound card has less priority unless you're obsessed with sound quality like me. What I like the most about my system is the 400-dollar 5.1 sound system so I cant live without a good sound card.
In Dharmaboy's build, if you move $100-150 from mb/water cooler/OS to video card, you can easily get 50% or more fps.