I have a four tier strategy, based on the fact that discs are cheap. I call it 6666 as in 6 inches, 6 feet, 6 miles and 6 thousand miles. I developed it based on a need to backup several hundred GB to few TB of data with respect to the privacy but still allowing sharing with my family.
Tier 1: 6 inches
RAID 1 in my desktop All important files that cannot be duplicated are stored on RAID 1 disk array. If a disk fail I have a local copy immediately available for restore
Tier 2: 6 feet
Local online backup. Each important file is duplicated between my desktop and my file server. On file server the files are stored on a RAID 1 array. If my local desktop break completely (e.g. motherboard burns out and takes the disk controller and disks with it) I have the file server immediately available for restore. The replication is done on a scheduled and manual basis.
Tier 3: 6 miles
All important files are from time to time copied to a portable hard disk that is stored in a safety deposit box. This disk is updated every few weeks/months. If my house burns down I have majority of my data locally available for immediate restore. The data which are not present are restored from the remote backup in tier 4.
Tier 4: 6000 miles
All important files are remotely copied to a file server at my parents house on a different continent. It servers, two purposes. If for some reason my immediate locality is affected by natural disaster (fire, flood, tornado), my files are safe. Also if my parents wants to see my HD videos of my kids, they have them locally available and I don't have to share it with them. The replication is done on manual basis.
I have experimented with many different technologies how to implement this strategy (CrashPlan, HW RAID, SW RAID, rsync, etc.) and this is what I have settled on since it is foolproof, non proprietary and can be implemented (in case of remote backup) by non techie.
Tier 1: SW RAID using mdam on Ubuntu 64b Desktop encrypted using LUKS
Tier 2: SW RAID using mdam on CentOS 64b Server encrypted using LUKS. Populated manually using rsync every time I upload new pictures and videos to server. Home directories and documents are rsynced automatically every few hours.(Before I used CrashPlan)
Tier 3: Truecrypt on portable HDD populated using rsync manually to review changes.
Tier 4: PogoPlug modded using http://www.google.com/search?client=ubuntu&channel=fs&q=pogoplug+arm+linux&ie=utf-8&oe=utf-8 to provide remote ssh server and local Samba server. Data are copied manually using rsync every time I update tier 2. The local Samba is used for local sharing of the multimedia (pictures, videos) at the destination. The beauty of this solution is that is is completely plug and play and my parents don't have to know anything about technology. I gave them 2 pieces of hardware (pogoplug and hdd), they plugged in 4 cords at their location (1 network, 1 usb, two power) and I configured their router.
Cost
Tier 1: 1 extra internal HDD (assuming desktop computer is already present)
Tier 2: 1 extra internal HDD (assuming you are already running filer server for your household)
Tier 3: 1 portable HDD
Tier 4: 1 Pogoplug ($30 on sale) + 1 portable HDD
If you start with 3 TB disks in each computer. This solution required 4 extra 3 TB disks + 1 pogoplug and little bit of manual effort.