Check out the DFI boards if you overclock, since they are proven to be the best overclockers. Corsair RAM is good, but compare prices and performance to OCZ as well. See if you can get a dual core system. And check out AM2, since socket 939 will be obsolete soon and AM2 will provide you a longer upgrade path.
But, you may want to consider an Intel Conroe compatible motherboard, as they may provide more performance in the future.
The graphics card is fine; however, if you will NOT use Sli, then consider the ATi 1900XTX, as it is faster than a single 7900GTX.
For more performance, you can consider RAID by getting two smaller HDDs and placing them in striping mode (a few dollars more than one HDD)
From your current setup, you can expect really nice performance. Also, you WILL NEED extra cooling if you plan to overclock, as OCing WILL use more electricity, and thus produce more heat. I suggest Zalman, Thermaltake, Scythe, and Thermalright.