How do you feel about rolling your own, for God, country and savings?

Zonk mentioned the Proliant Microserver. It's a tiny, quiet little thing with 4 x SATA slots for your drives and some extra external ports for expansion. They also running regular offers for cashback on purchase. Current one in the UK is £100 back off the £160 purchase price of the machine. I'm betting there will be similar deals in the States. The box is stupid cheap either way.

4 x Seagate 3TB drives gives you 12TB raw for around $400

4 x Seagate 4TB drives = 16TB for around $640

So that's 12 or 16 raw TB for $500 OR $750 ?

On my Microserver I installed FreeBSD to a USB stick and boot from that. Then I configured ZFS from the command line and created my pool.

If you don't want to fiddle around with FreeBSD, there is FreeNAS which does all the goodness in the background and gives you a nice GUI for configuration.

The benefits of a little multi-purpose box, though, is that you can have it do other things in addition to providing NAS. Mine grabs torrents, handles networked security cameras in the house, lets me get back into the LAN when I'm travelling etc. Also it's extremely low power, which saves a few pennies when you're running it 24/7 for the year.

One thing I'll get around to doing eventually is trickling an entire mirror of the data to Amazon S3 storage for a proper offsite backup.