Samsung has announced a one terabyte eco-friendly hard drive with low power features, partly because it only uses three platters. The press release says: "The EcoGreen F1 will launch in the second quarter of 2008 with a MSRP of $199."
That's currently a good price for what it offers: you can get a 1TB drive for $200 from Amazon.com but you can also pay up to $600. (The cheapest is around £120 at Amazon.co.uk.) By next summer, however, prices will be lower.
A 1TB drive will store about the same as 1,500 CD-R discs, but you'll still need backups.