RAID 0 is the best for gaming. You're not going to see an increase in FPS or anything, but levels will sure as hell load faster. Unless you're playing every MMORPG and FPS on the market and you need the storage for all ur games, RAID 0 would best suit you.
But like TunaSoda said, RAID 0 is definitely not for storage. Don't put anything important on the array.
Personally I use 2 Western Digital Raptor 36Gb Hard drives in RAID0 and then a 200GB hard drive for storage.
The raptor drives are extremely fast and will give you the best hard drive performance for gaming. The 76GB Raptors are even faster than the 36GB due to better hardware. These drives are more expensive, but the performance has impressed me enough to justify it.
TunaSoda is correct though, a RAID0 volume is meant for speed not stability. I had my RAID0 crash once earlier this year, but my important stuff was on my 200 gig.
Bottom line is if you want to do RAID0 I'd suggest you have a minimum of 3 hard drives. Two for RAID to run your OS and one big drive to do storage.