Hey dude, i was in the same boat as you a few days ago. I was trying to figure out what to get for a budget yet make sure it would last a couple years (Ddr3 for example). Before you build your system you have to ask yourself what do i want for Gaming performance. If You are willing to spend the extra cash later on i would get a Evga 790i Sli mother board. And either buy one awesome card now and Sli it later when u get payed again or buy two cheaper cards and be happy with that. A good example of your choices would be getting 2 9600gt's now and keeping them. Or getting a 9800Gx2 now and puting in another later. Both perform well, but the 9800gx2 in sli is beastly. There is another option and that is wait for the 9900's in july, but if your like me i can never wait when it comes to a new build. As for a hard drive i would go for 2x250gb Barracudas in Raid. I recently found out that that mobo supported raid and i hear its great, plus the hd's only go for about $69.99 each.
The Mobo, pricey but will last a while, also it is hard to find a cheap board that supports DDr3:
Newegg.com - EVGA 132-CK-NF79-A1 LGA 775 NVIDIA nForce 790i Ultra SLI DDR3 ATX Intel Motherboard - Retail