I have a EVGA X58 SLI LE MOBO, built my compter around the mobo and processor, hard drive and the memory the most importent things, wow almost forgot cpu heatsink very very importent, you want to keep that baby cool. also power supply, you got to have enough power to feed the beast. I wouldnt go under 800 watts, if you want to 2 way SLi it can handle it 3 way sli go at least 1000 watts. its always better to have extra power then not enough. Also go modular, the cables you dont need you can leave out.
Memory: DDR3 1600 MHZ or faster. I think no less then 6 gbs, although this mobo take 24 gbs of memory. the thing I like about my mobo is that I can sli or crossfire it so I have double the choices, nvidea or ati, and I have never had a problem with my computer, other then video card cant handle Crysis real well and runs real hot. I got a gtx 275, plays all the cods no problems though. GTX 460 or bigger Go ful tower you what to have lots of room for everything and good air flow. I got the CoolMaster Half.
the best thing you can do is go to Newegg.com open a account and start shopping, check your shopping cart to see how much you are spending, if to much start cutting back to the essentials. Dont skimp on the heatsink though, get the best one that will keep in nice and cool, VERY, VERY important!!!!!
Anyway I hope this helps a little. Take the time to really check everything out for your needs
SABREEYES