Whether you use Windows or OS X, Look at one of the configurations of the OWC Mercury Elite Pro Qx2 solutions. http://eshop.macsales.com/shop/hard-drives/RAID/Desktop/
Other folks like the QNAP RAID boxes.
RAID 0 (striping) is an excellent way to make access fast - and also an excellent way to lose all of your data should one drive in your RAID array crash.
RAID 1 (Mirroring) is slower access than RAID 0 but offers a level of redundancy & safety ( your data is copied onto two drives when it is written to the RAID array) in case a drive crashes. This also menas that if you have 4 2 TB drives you can only use 4TB for capacity.
RAID 5 is more ideal for general use as it combines striping (for speed) with parity checking. This means you can one of the four drives can crash but your data is safely distributed throughout the other three drives. In my hypothetical 4 x 2TB RAID array this also means you have greater capacity than in a RAID 1 set up , 6TB instead of just 4TB. It is not as fast as RAID ) but a lot more secure (in case you haven't notice, RAID 0 isn't at all safe.) Two warnings about RAID 5: If two drives at once crash your data is hosed; and the closer to full capacity you are in the system the longer the directory file structure rebuild takes.
RAID 10 (also known as RAID 1+0) combines Striping (speed) and Mirroring (redundancy) which keeps your data safer, but at the price of speed (compared to RAID 0 and RAID 5) and capacity (in the 4 x 2TB hypothetical , only 4TB are used for storage.
One more note: even though RAID 1, 5 & 10 systems have built in redundancy, that is not the same as backup, and you need to back your data to a second (and ideally third) place. A second (or Third ) RAID array can be part of your back up solution but storing your vital data on a single RAID array is an avoidable accident waiting to happen.