While most netbooks come with a decent-size hard drive, you can always use more. Tiny USB thumb drives can help in a pinch but they don't pack much extra storage space, which is why Western Digital's line of My Passport Essential portable hard drives are a perfect big-time storage supplement for netbooks. They're the smallest available from WD, come in a variety of colors and range in size from 250 GB to 640 GB. In case you're storing sensitive materials, like info on Area 51 or plans to crash the next White House party, files can be password-protected and encrypted. WD also bundles their SmartWare software for automatic and seamless backup with a control-center view of all your data.
Price: About $90 (for 250 GB)