If you want a fast system drive and have cash to burn, look into SSD's. There are a number of reasonably priced SSD's on the market now.
+1 I'm running 2 SSD's in a RAID 0 and the speed can't be beat. I would recommend additional drives for storage though.
Also I'm a big fan of EVGA's X58 mobo. I've been running one ever since it was released and it is rock solid and insanely fast
My current rig
EVGA x58 Mobo
Intel I7 920
6GB RAM
Dual 120GB SSD's in RAID 0 (System Partition)
Dual 75GB Raptors in RAID 0 (Storage for System Partition)
Dual 150 GB Velociraptors in Raid 0 (Program Install Partition)
2 1.0 TB drives for Storage
2 DVD burners
Dual EVGA GeForce 260's in SLI
Samsung TOC 26" LCD