Backblaze
For Windows and Mac users, Backblaze backs up all of your internal, USB-, and Firewire-connected drives. It's not designed to be supplemental storage, but rather an automatic backup of everything on your hard disk except for the operating system, applications, and temporary files. As such, there's no interface to pick and choose which files to back up, which makes it a simpler tool to operate. Network drives, including NAS devices, are excluded, and Backblaze also skips files larger than 4 GB.
The initial backup occurs at the rate of 2 to 4 GB per day, and a quick restore can be accomplished by having Backblaze send, via overnight courier, a USB drive containing your latest data.
Backblaze costs $5 per month per computer, or $50 per year.
Carbonite
Carbonite offers a comprehensive, no-limit backup plan which encrypts and then backs up the entire Documents and Settings folder for Windows users, or the Users folder for Mac users. Once installed, the Carbonite software tweaks the file system such that the icons for backed-up files are displayed with a green or yellow dot to indicate whether the file has been backed up or is pending backup.
From your computer, you can access the Carbonite Backup Drive to see what's in the archive and to restore files. You can also log into your password-secured account from the Carbonite Web site, either from another computer or from an iPhone, iPod Touch, or BlackBerry.
Subscriptions are available for $54.95 per year, $99.95 for two years, $129.95 for three years, or $199.95 for five years.