Post it here so we know it's all compatible?
http://www.newegg.com/Product/Product.aspx?Item=N82E16814162022&cm_re=nvidia_GeForce_9500-_-14-162-022-_-ProductThis graphics card is quite a bit cheaper, while still in a good range for speed. It has a smaller bit size, but twice as much memory, and has GDDR2, which is supposedly better than DDR3http://www.newegg.com/Product/Product.aspx?Item=N82E16820141300Even if you don't go for the above graphics card, I would personally go for this ram. Its basically the same thing, for about $15 cheaper (You would have to get two of them though).
that 780W psu you linked is 630W. also the link to your motherboard is the one for your cpu.oh and costs about the same, but is a little better than the video card you picked out http://www.newegg.com/Product/Product.aspx?Item=N82E16814161296
Get a better power supply.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817341022This. Now I don't know how much room you have in that case, so I picked out a modular psu just in case. That and it looks neat, not that it really matters.
Is 550w enough to power it though? I was told before that I would need to upgrade even my 630w.