Take a look at one of these units:
Black Anyware ME-601SD Docking Station, w/ One-Touch Backup, Supports 2.5in/3.5in SATA I/II HDDs
You can add any type of SATA OEM raw hard drive to this unit in any OS using USB or eSATA. No tools required. A new OEM SATA 500 Gig drive will run you between $60 and $70. (See Newegg Internal Hard Drives
)You can use this unit to clone your existing drive, backup the drive, backup files or anything else you want. You can then remove the backup drive and move it to another computer or to outside storage (bank safe deposit box). You can move the unit from one computer to another and backup another computer just by changing the hard drive in the Dock.
Very versatile backup or additional storage device.
Thermaltake also makes a unit which does the same thing only it it $10.00 more expensive.