I'm running an OpenSolaris server with one mirrored pair of drives for the operating system, and an eight-disk RAID-Z2 array (two drives worth of redundancy) for the main storage pool. All drives are 500 GB, half Seagate Barracuda and half WD Caviar Blue.
In my experience, both the Seagate and WD drives are very quiet - the case fans are noisier than the entire drive array. I'm not sure I'd go with the Caviar Green drives though - they have a tendency to go to sleep very easily, resulting in lots of start/stop cycles (bad for longevity). Which costs more - the extra electricity or the cost of replacing a drive?
Why OpenSolaris?
ZFS. No need to worry about partition sizes, instant filesystem snapshots, and every block written to disk is checksummed. Corrupted data is detected automatically, and reconstructed if you run redundant drives or configure a single drive to write multiple copies of disk blocks. ZFS also integrates nicely with CIFS for Windows file shares, NFS for Linux/BSD/Solaris shares, and iSCSI for SAN-type functionality (sharing a volume that a remote system sees as a disk).
You still need a backup solution though - as many have pointed out,
RAID is not backup. If your system fails catastrophically, or gets stolen, or is lost in a fire, you need something to fall back on.
In addition, OpenSolaris isn't exactly friendly to the average computer user, and Linux has better hardware support. Even if you're a Linux guru, it can be a bit of a culture shock, but I've found it worth adding to my home network anyway.
Here's a good starting point on
setting up a home ZFS system.