Who needs to back up to an external drive when you can back up to the cloud? MiMedia (various pricing) offers backup of all your important media files to secure servers on the Web for a monthly or yearly fee. Some backup solutions (such as Carbonite) bypass backing up media files altogether, unless you specifically instruct them to do so. MiMedia is idiot-proof: Just download, install, register your account, verify your e-mail address, then choose recommended settings and go.
I like how easy it is to set up and configure MiMedia. The recommended settings automatically back up the My Photos, My Music, My Videos and My Documents folders in their entirety. The basic setting skips the My Documents folder, and there's also an Advanced setting that can specify additional backup folders.
MiMedia also lets you know exactly how large your backup will be as it is performed, which is useful as you select your free trial (and pay plan) as the backup occurs. If you have many gigabytes of files, you're going to want the higher plan. In the case of a large backup, one really nifty feature is the Shuttle Drive service. Many gigabytes will take hours and hours and hours to back up over broadband; MiMedia offers an alternative. They'll ship you a hard drive in a few days (provided you give them your credit card information as security). Plug in the drive with MiMedia up and the backup starts; then, ship them the drive free. While waiting for your drive to get to your place, MiMedia will start backing up the traditional way.
Other than backup, MiMedia takes it one step further: You can access your backed-up files from any Web browser, whether MiMedia is installed or not, or on any iPhone, iPod Touch, or iPad with the free MiMedia app. Note that this backed-up version will sync between all devices with MiMedia installed, but the original source file pre-backup does not sync. Once you have MiMedia installed, it's best to update the file from the MiMedia app directly from then on so there's no confusion or versioning issues. You also won't have to run the backup ever again at that point as long as MiMedia stays running. Also note that rather than preserving your original Windows media folders (such as My Documents, etc), MiMedia re-sorts everything into its own document, music, videos and photo folders. However, the original files in their original ordering can be found in the Backups section.
I tried the MiMedia app on an iPad running iOS 4.2 and an iPhone 3G running iOS 3.3.2. These apps include streaming ability for your movie or music files, which can come in handy on trips, though the app balked at a half-hour AVI movie file encoded with H.264 (though it played fine in the web version.) I discovered one bug in the iOS apps: attempting to start a backup with no media files present (perhaps with the intent of adding media files on the fly) causes these apps to crash. The developers are aware of the issue, and recommend not starting a backup unless at least one media file is present in one of the chosen folders.
MiMedia's chief competitor in this cloud-based filesharing arena is the ubiquitous DropBox. DropBox does not offer automatic backup of folders; you must copy important files to your DropBox folders by hand, which takes a bit more knowledge. On the upside, DropBox Basic offers 2GB free in perpetuity and acts as a folder in Windows Explorer rather than requiring you to browse for your backed-up files from the web. Comparison of pay plans shows that MiMedia offers twice as much space for the same fee ($99/year buys you 50GB at DropBox but 100GB at MiMedia) and 2.5 times the space in the next tier ($199 for 100GB at DropBox; $195 for 250GB at MiMedia).
Note that MiMedia won't back up an image of your entire hard drive or hard drives, nor will it back up your registry so that licenses for apps are preserved, for example. You'll need to seek out a total system backup app (or just use the one included with Windows) for that. Backing up specific critical media files and doing away with the fragility of mass storage is a good idea in general, and MiMedia is a less-expensive alternative to DropBox.