Based on my experience with Asus, I'd recommend going with one of their competitors for your mainboard. Try the Gigabyte UD3P
as a reasonably priced alternative at $125 after rebate.
Next, spend a bit more money on the GPU and get a GTX 260
for $160 after rebate. If you can spend it, you'd be very wise to pick up the GTX 260 Core 216
. It's worth it for the extra shader processors.
And waverrider had the right idea about cases - you can find some better options out there for about the same money, but that's a much more subjective issue, so I'll not comment. Enjoy!