Never trust a single piece of hardware. Never trust two either.

For me:

  - SANs/NASes make use of ZFS-Z2 or RAID 6. But, RAID is NOT a backup!
  - Have two or four separate backups in rotation (depending on how critical
  the data is). Half of which are located at a local bank's safety deposit box. Boxes
  typically run less than $75 per year. Work with the branch manager to get a
  top-level box for improved flood mitigation.
  - Each week, make a trip to the bank and switch them out.
  - These are awesome transports for this approach:
  http://www.amazon.com/Silicon-Forensics-Drive-Transporter-Classic/dp/B002IY6B9U
  - Careful of SSDs in RAID, they tend to all fail within a short period of time
  due to their reliable point of failure with writes.

If it is critical data, I get a little more crazy. ;) If the cloud is more your style, you might check out SpiderOak (but, again, unless treated as a backup it should not be used as such). I make use of this as well.