RAID 10 is a viable option, as mentioned.
Here's what my RAID 10 does, in regard to speeds: http://www.techpowerup.com/forums/sh...3&postcount=33
With RAID 10, you "lose" half of the HDDs size due to the mirroring and you need 4 HDDs minimum: it has good read and write speeds.
With RAID 5, one of the HDDs will be used for parity and you'll need 3 HDDs minimum: it has good read speeds but bad write ones.
Check this video: http://www.youtube.com/watch?v=TuwjadbtUCY
for better info.