I too would recommend the 930, a killer deal at today's pricing. All of the main-boards look fine, you might want to also look at intel's; my experience with driver / firmware updates from asus has been pretty disappointing ( a recent product they offered had no less than 13 firmware updates since release last fall -what are they doing???).
As far as drives:
system - raid-1 with fast 10k rpm drive, velociraptors are a nice fit here. i like the 150gb drive's single platter design and simplicity
storage - stay away from raidi5, unless you absolutely need a single volume beyond 2TB. i prefer raid-1 here with it's superior write and read performance.
scratch - no idea, actually! i was preferring the SSD option, until I read Jeff Schewe's description of his system - I was suprised at the potential size requirements of a scratch volume...... obviously, the faster the better here....